Bede's Ecclesiastical History of England, ed. by A.M. Sellar, , at sacred-texts.com
EDWIN being slain in battle, the kingdom of the Deiri, to which province his family belonged, and where he first began to reign, passed to Osric, the son of his uncle Aelfric, who, through the preaching of Paulinus, had also received the mysteries of the faith. But the kingdom of the Bernicians—for into these two provinces the nation of the Northumbrians was formerly divided —passed to Eanfrid, the son of Ethelfrid, who derived his origin from the royal family of that province. For all the time that Edwin reigned, the sons of the aforesaid Ethelfrid, who had reigned before him, with many of the younger nobility, lived in banishment among the Scots or Picts, and were there instructed according to the doctrine of the Scots, and were renewed with the grace of Baptism. Upon the death of the king, their enemy, they were allowed to return home, and the aforesaid Eanfrid, as the eldest of them, became king of the Bernicians. Both those kings, as soon as they obtained the government of their earthly kingdoms, abjured and betrayed the mysteries of the heavenly kingdom to which they had been admitted, and again delivered themselves up to defilement and perdition through the abominations of their former idolatry.
But soon after, the king of the Britons, Caedwalla, the unrighteous instrument of rightful vengeance, slew them both. First, in the following summer, he put Osric to death; for, being rashly besieged by him in the municipal town, he sallied out on a sudden with all his forces, took him by surprise, and destroyed him and all his army. Then,when he had occupied the provinces of the Northumbrians for a whole year,not ruling them like a victorious king, but ravaging them like a furious tyrant, he at length put an end to Eanfrid, in like manner, when he unadvisedly came to him with only twelve chosen soldiers, to sue for peace. To this day, that year is looked upon as ill-omened, and hateful to all good men; as well on account of the apostacy of the English kings, who had renounced the mysteries of the faith, as of the outrageous tyranny of the British king. Hence it has been generally agreed, in reckoning the dates of the kings, to abolish the memory of those faithless monarchs, and to assign that year to the reign of the following king, Oswald, a man beloved of God. This king, after the death of his brother Eanfrid,advanced with an army, small, indeed, in number, but strengthened with the faith of Christ; and the impious commander of the Britons, in spite of his vast forces, which he boasted nothing could withstand, was slain at a place called in the English tongue Denisesburna, that is, the brook of Denis.