Bede's Ecclesiastical History of England, ed. by A.M. Sellar, , at sacred-texts.com
At this time, the brave and ambitious king, Ethelfrid, governed the kingdom of the Northumbrians, and ravaged the Britons more than all the chiefs of the English, insomuch that he might be compared to Saul of old, king of the Israelites, save only in this, that he was ignorant of Divine religion. For he conquered more territories from the Britons than any other chieftain or king, either subduing the inhabitants and making them tributary, or driving them out and planting the English in their places. To him might justly be applied the saying of the patriarch blessing his son in the person of Saul, "Benjamin shall ravin as a wolf; in the morning he shall devour the prey, and at night he shall divide the spoil." Hereupon, Aedan, king of the Scots that dwell in Britain, being alarmed by his success, came against him with a great and mighty army, but was defeated and fled with a few followers; for almost all his army was cut to pieces at a famous place, called Degsastan, that is, Degsa Stone. In which battle also Theodbald, brother to Ethelfrid, was killed, with almost all the forces he commanded. This war Ethelfrid brought to an end in the year of our Lord 603, the eleventh of his own reign, which lasted twenty-four years, and the first year of the reign of Phocas, who then was at the head of the Roman empire. From that time, no king of the Scots durst come into Britain to make war on the English to this day.