Oswald and Aidan
This excerpt from Bede's Ecclesiastical History (Book 3, chapter 3) primarily describes the evangelistic efforts of Northumbrian King Oswald, "a man beloved by God," and his bishop, Aidan, but references to the Easter date controversy and to the topography of Lindisfarne allude to Bede's broader interests.
The same Oswald, as soon as he ascended the throne, being desirous that all his nation should receive the Christian faith, whereof he had found happy experience in vanquishing the barbarians, sent to the elders of the Scots, among whom himself and his followers, when in banishment, had received the sacrament of baptism, desiring they would send him a bishop, by whose instruction and ministry the English nation, which he governed, might be taught the advantages, and receive the sacraments of the Christian faith.
Nor were they slow in granting his request; but sent him Bishop Aidan, a man of singular meekness, piety, and moderation; zealous in the cause of God, though not altogether according to knowledge; for he was wont to keep Easter Sunday according to the custom of his country, which we have before so often mentioned, from the fourteenth to the twentieth moon; the northern province of the Scots, and all the nation of the Picts, celebrating Easter then after that manner, and believing that they therein followed the writings of the holy and praiseworthy Father Anatolius; the truth of which every skillful person can discern. But the Scots which dwelt in the South of Ireland had long since, by the admonition of the bishop of the Apostolic See, learned to observe Easter according to the canonical custom.
On the arrival of the bishop, the king appointed him his episcopal see in the isle of Lindisfarne, as he ...