Early records and chronicles (5th-15th century)

Records from the earliest known mentions of Slavic religion up to the end of middle ages, organised by the group involved and by the age of the record. "Sources of Slavic pre-christian religion" mentioned in the academic research list contains many of the following records translated into English, but it is incomplete and fairly hard to come by.

West Slavic

Czech

First slavonic legend about saint Wenceslaw (Život svatého Václava; half of 10th century) - Czech
Paragraph 1 (mention of postřižiny, the first haircut ritual):
There was a ruler in Bohemia by the name of Vratislav, and his wife was named Drahomíra. And their firstborn son was born, and at baptism they gave him the name Václav. Když povyrostl a bylo třeba mu udělit postřižiny, his father Vratislav invited to them a certain bishop with his notary and with his clergy. In the temple of holy Mary a mass was held for him, and then the bishop took the boy, put him down on the corner of the step in front of the altar and blessed him with the words: "Lord Jesus Christ, bless this boy, like you blessed all your righteous." And so with the blessing his hair was cut.

Gumpold's legend (Život svatého Václava; 980) - Czech, Latin
Chapter 7 (mention of offerings and animal sacrifices):
But the tribes, which were placed under his royal power by the law and according to ancient customs, were unstable and swayable in the newly accepted faith. So when this youth of divine talent watched, how even the lords would meet more often in the year in accursed shrines and by the altars of pagan demons, to bring sacrifices to foreign gods there, even though he was often invited to participate in the disgusting feasts, during which the sacrificial animals were presented, he still not only rejected the forbidden feasts - since above all he desired the feasts of the heavenly table - but also avoided even the everyday encounters with feastgoers tainted by the devil's filth as thoroughly as possible.

Second slavonic legend about saint Wenceslaw (Kniha o rodu a utrpení svatého knížete Václava; end of 10th century) - Czech
Chapter 7 (mention of offerings and sacrificial feasts):
Even to the people, who still lived in the old pagan way, he would give the good teachings of the new faith. And when this blessed youth saw how they keep going to the idolatrous shrines in their ignorance and offer sacrifices to foreign unknown gods, he would then avoid visiting and participating in these godless sacrificial feasts, despite being often invited, because he wished above all to become the participant of the heavenly feast, rather than taint himself with the devilish abomination of these sacrifices.[...] Some people, slightly more susceptible to the right path, leading to the highest good, he would remind with a sweet voice and bring them back by promising them the gifts of heavenly mercy, that they would renounce pagan idols which they allowed themselves to be tricked by, and come closer with faith to the truthful promise of divine intention.
Chapter 10 (Slavic rituals):
Across the whole country, she estabilished idolatrous shrines and turned the entire land to them, brought them sacrifices and forced her son to them.
Chapter 11 (persecution of non-christians):
Already by then, several uprisings in the pagan lands were defeated under his rule through divine favour, and the joyful growth of the catholic religion renewed.

Christian's legend (Vita et passio sancti Wenceslai et sanctae Ludmilae avae eius/Život a umučení svatého Václava a jeho báby svaté Ludmily; Kristián, 994) - Latin, Czech
Chapter 2 (national mythology, mention of idols and sacrifices):
Afterwards, being troubled by plague, they went to a certain seer for a hopeful advice and a prophetic answer. Receiving it, they founded a castle and name it Praha. Then they found a very foreseeing and thoughtful man, whose work was the culturing of fields, by the name of Přemysl, according to the vision of the seer made him their ruler or stewart, and gave him the aforementioned seer maiden as a wife. Delivered from the disaster and plague afterwards, following this ruler they would put his descendants into their leadership, served the idols of demons and would surrender themselves fully to pagan sacrificial rituals, until finally the rule of the country went to one from the kin of these dukes, by the name of Bořivoj.
Chapter 6 (destruction of temples):
He demolished prisons, then in his mercy tore down gallows, that until then were used for executing people, and razed pagan temples to the ground.

Chronicle of Czechs (Chronica Boemorum/Kronika Čechů; Kosmas, 1119-1125) - Latin (original manuscript), Latin (German commentary), Czech
Chapter 1 (national mythology, mentions of Slavic spirits and gods (usually under Roman names); example of an oath, example of magic):
1.4 - The oldest of them was Kazi, who far exceeded Medea of Colchis in the matter of herbs and divination, as well as Asclepius in healing, as she often caused Fates to give up their unending work, and forced even fate to obey her will through magic.[...] When she was taken to the ruler dull and unwise folk to bow to spirits ruling the mountains (Oreads), forests (Dryads) and trees (Hamadryads), and venerate them; she also estabilished an entire superstitious teaching and taught idolatrous rules; and so until today, many villagers are like pagans: one venerates the springs and fire, the other bows to groves, trees or stones, while another gives sacrifices to hills or mountains, and the next prays to deaf and mute gods he made himself, and asks them to protect his house and himself.
1.8 - And when they finished the journey and were nearing the castle, the lady came out to greet them, surrounded by her courtiers; they went into their home holding hands, ate from the gifts of Ceres and Bacchus, and gifted the rest of the night to Venus and Hymenaeus.
1.9 - Přemysl has finished the days, when he would set rights and laws, and was taken to the son-in-law of Ceres, who he venerated as a god in his life.[...] When his life was torn in half by Fates, Křesomysl was put on the throne.
1.10 - With the god Mars and my ruler Bellona, which has given me various blessings, as witnesses, I swear on the hilt of the sword in my hand, that I will give mothers puppies to nurse instead of their infants.
1.11 - Know, that the witches or demons of Czechs gained advantage over our seers, so ours will all perish and the victory will go to Czechs. So that you may escape the annihilation in the end, cut off both the ears of the enemy that you face first, then hide them in your wallet; then draw a line in the shape of a cross on the ground, between the horse's legs. Because that is how you'll loosen the invisible binds, with which the gods' wrath will tie your horses, so they would weaken and fall, as if exhausted after a long journey. And immediately after sitting on the horse, flee, and even if you hear loud thundering behind you, never look around, but hurry even more; and so only you will barely escape. Because the gods that would accompany us into battles have turned to aid your enemies.[...] And like always, the unbelieving people more susceptible to evil, when their strength and good characteristics leave them, turn immediately to the worse aspects and injustice, and these people were no different, devoted to false idolatry and even more to lies, they were now desperate over their strength and arms; and so they turned to an old seer to request her aid, to tell them, what to do in such a danger, or what result may the next battle have. She was full of the seeing spirit and did not delay them with riddles. "if you want", she says, "to reach the glory of victory, you first need to fulfill the commands of the gods. Therefore sacrifice to them a donkey, so that their protection will be with you. This sacrifice is ordered by the highest god Jupiter, Mars himself and his sister Bellona, as well as Ceres' son-in-law". So they found a poor donkey, killed him, and cut him into a hundred thousand pieces, which were immediately eaten by the whole army.
Chapter 3 (persecution of non-christians, mentions of specific rituals and holidays):
3.1 - And like in his youth, when he would already give all his hope under God's protection, right at the beginning of his rule he was filled with zealousy for the christian religion, and he chased out all the wizards, magicians and seers from the land; he also ordered the cutting down and burning of groves and trees, that the common people venerated in many places. Similarly, the superstitious customs, which the villagers, still half-pagan, would keep on the tuesday or wednesday of Pentecost by bringing gifts and offerings to the springs adn sacrifices to evil spirits, as well as burials that would occur in forests and fields, and games that occured on crossroads according to the pagan ritual for the peace of souls, and finally also godless pastimes, which they would unrulily perform over their dead, calling empty shadows with masks on their faces, the good duke got rid of all of these abominations and other godless fabrications, so that they would no longer occur among God's people.

Oportet nos fratres (mid-12th century) - Czech
Part 1 (Mention of idols):
Because the inhabitants of this land lived without laws until the reign of the roman emperor Henry, they didn't know the heavenly King, as if they had no wisdom, they did not care that they're the creation of such a great maker, and they served the deaf and mute idols, wandering far from truth.
Part 15 (Mention of idols and sacrifices): You are the worshippers of unclean idols and god-empty persecutors of almost all christians.[...] You estabilished holidays and celebrations to demons and not God, offered sacrifices to foreign gods and supressed everything, which leads to the true God.

Neplach's chronicle (Summula chronicae tam Romanae quam Bohemicae/Krátká kronika římská a česká; Jan Neplach, 1360) - Latin
Year 894 (National mythology, mention of the worship of "Zelu"):
We begin with the acts and deeds of the dukes and kings of Bohemia, some of whom were pagans, and so caring at what time or year they ruled is unnecessary. They had an idol, which they worshipped as their god, who they called Zelu. Ignoring the matters of these virgins, mentioned in the Chronicle of the Czechs, only Libuše must be spoken of briefly.

Dalimil's chronicle (Rýmovaná kronika česká tak řečeného Dalimila; 1314) - Czech, German (non-literal translation, 1342-1346)

Homiliary of Opatovice (Homiliář opatovický; 12th century) - Sermons 5, 30, 52, 79, 84, 85, 104, 122, 131; canons 135. Latin (original manuscript), Czech (partial)

Life of Saint Adalbert of Prague (Vita s. Adalberti episcopi Pragensis/Život svatého Vojtěcha Pražského; Jan Kanapariusz, 10th century). German

Wilhelm from the land of Slavs (Wilhelm von Wenden/Vilém ze země Slovanů; Oldřich z Etzenbachu, 13th century) - Fictional epic with mythological references; line 5210 (mention of Štěstěna, personification of luck). German

Astronomiarius (Klaret/Bartoloměj z Chlumce, 14th century) - Astronomy and astrology, line 776-777 (a record of the myth of 12 months). Latin

Glossarius (Glosář, Klaret/Bartoloměj z Chlumce, 1360) - Astronomy, mentions of Slavic spirits related to the sky and other beings. Latin/Czech, Latin/Czech with commentary

Ortulus phiziologye (Zahrádka fyziologie; Klaret/Bartoloměj z Chlumce, 1365) - Mentions of mythological beings.

Exemplarius auctorum (Klaret/Bartoloměj z Chlumce, 1366) - Sporadic mentions of slavic mythological figures. Latin/Czech

Polska gurom

Annals or chronicles of the glorious kingdom of Poland (Annales seu cronicae incliti Regni Poloniae/Roczniki czyli kroniki sławnego Królestwa Polskiego; Jan Długosz, 1455-1480) - Latin, pOwOlish

Polabian

Knýtlinga saga (Óláfr Þórðarson; 13th century) - Chapter 101 (first conversion of Arkona), 121 (sacking of Boku), 122 (Second conversion of Arkona, description of deities). Old Norse, Danish

Annals of Lorsch (Annales Laureshamensis; 8th-9th century) - Year 789. Latin
Annales Alamannici (8th-9th century) - Year 789. Latin

Chronicle of Thietmar of Merseburg (Thietmari Merseburgensis episcopi Chronicon; Thietmar, von Merseburg, 9th-10th century) - Chapter 1, 3, 4, 6, 7. Latin

Deeds of the Bishops of Hamburg (Gesta Hammaburgensis ecclesiae pontificum; Adam of Bremen, 1073-1076) - Chapter 2, 3, 4. Latin

Slavic chronicle (Helmoldi presbyteri Chronica Slavorum; Helmold, 12th century) - Chapter 1 (multiple gods addressed), 2 (mention of Svantovít). Latin
Arnoldi Chronica Slavorum (Arnold of Lübeck, 13th century) - Chapter 2, 5. Latin