Cædmon's story has one source -- Book IV, Chapter 24, of the Historia Ecclesiastica Gentis Anglorum (finished in 731) by the Venerable Bede (673-735), a monk of Jarrow in Northumbria. The following excerpt is rendered into modern English from A History of the English Church and People, translated by Leo Shirley-Price (Penguin Books, 1955): 245-47:

In this monastery of Whitby there lived a brother whom God's grace made remarkable. So skilful was he in composing religious and devotional songs, that he could quickly turn whatever passages of Scripture were explained to him into delightful and moving poetry in his own English tongue. These verses of his stirred the hearts of many folk to despise the world and aspire to heavenly things .... And although he followed a secular occupation until well advanced in years, he had never learned anything about poetry: indeed, whenever all those present at a feast took it in turns to sing and entertain the company, he would get up from table and go home directly he saw the harp approaching him. On one such occasion he had left the house in which the entertainment was being held and went out to the stable, where it was his duty to look after the beasts that night. He lay down there at the appointed time and fell asleep, and in a dream he saw a man standing beside him who called him by name. "Cædmon," he said, "sing me a song." "I don't know how to sing," he replied. "It is because I cannot sing that I left the feast and came here." The man who addressed him then said: "But you shall sing to me." "What should I sing about?" he replied. "Sing about the Creation of all things," the other answered. And Cædmon immediately began to sing verses in praise of God the Creator that he had never heard before, and their theme ran thus: "Let us praise the Maker of the kingdom of heaven, the power and purpose of our Creator, and the acts of the Father of glory. Let us sing how theeternal God, the author of all marvels, first created the heavens for the sons of men as a roof to cover them, and how their almighty Protector gave them the earth for their dwelling place." This is the general sense, but not the actual words that Cædmon sang in his dream; for however excellent the verses, it is impossible to translate them from one language into another without losing much of their beauty and dignity. When Cædmon awoke, he remembered everything that he had sung in his dream, and soon added more verses in the same style to the glory of God. Early in the morning he went to his superior the reeve, and told him about this gift that he had received. The reeve took him before the abbess, who ordered him to give an account of his dream and repeat the verses in the presence of many learned men, so that they might decide their quality and origin. All of them agreed that Cædmon's gift had been given him by our Lord, and when they had explained to him a passage of scriptural history or doctrine, they asked him to render it into verse if he could. He promised to do this, and returned next morning with excellent verses as they had ordered him. The abbess was delighted that God had given such grace to the man, and advised him to abandon secular life and adopt the monastic state, And when she had admitted him into the Community as a brother, she ordered him to be instructed in the events of sacred history. So Cædmon stored up in his memory all that he learned, and after meditating on it, turned it into such melodious verse that delightful renderings turned his instructors into his audience. He sang of the creation of the world, the origin of the human race, and the whole story of Genesis. He sang of Israel's departure from Egypt, their entry into the land of promise, and many other events of scriptural history. He sang of the Lord's Incarnation, Passion, Resurrection, and Ascension into heaven, the coming of the Holy Spirit, and the teaching of the Apostles. He also made many poems on the terrors of the Last Judgement, the horrible pains of Hell, and the joys of the kingdom of heaven. In addition to these, he composed several others on the blessings and judgements of God, by which he sought to turn his hearers from delight into wickedness, and to inspire them to love and do good. For Cædmon was a deeply religious man, who humbly submitted to regular discipline, and firmly resisted all who tried to do evil, thus winning a happy death."

This monastery, then named Strenæs-hale, was situated about fifty miles south of Jarrow on the coast of Yorkshire. The abbess who assisted Cædmon was named Hild; she founded the monastery and ruled it from 658 to 680. A reconstruction of the Sutton Hoo harp, which would have resembled the one from which Cædmon fled and later, presumably, used, is shown in Rupert L. S. Bruce-Mitford, "The Sutton Hoo Ship-burial," Proceedings of the Royal Institute of Great Britain, 34 (1950): plate II B. Old English poems of the sort Bede mentions as of Cædmon's laterauthorship survive, such as Adreas, Christ I-III, and Christ and Satan, but Francis P. Magoun, Jr., in his article "Bede's Story of Cædman: The Case History of an Anglo-Saxon Oral Singer," Speculum 30 (1955):49-63, offers good grounds for thinking none belonged to Cædmon. We do not know when Cædmon was born or died, but his conversion to a poet must have taken place sometime in Hild's rule of the Whitby monastery.

• Stanley, E. G.. “Cædmon (fl. c.670).” Oxford Dictionary of National Biography. Ed. H. C. G. Matthew and Brian Harrison. Oxford: OUP, 2004.