The Chronicle of Croyland, usually attributed to Ingulf who lived in the eleventh century, was later found to be started as early as 655.  The unknown author(s) is now referred to Pseudo-Ingulf.  The current MS dates from the 13th or 14th century and the originals have been lost:

The renowned king Edward having filled the measure of his days, his son Athelstan succeeded him. Anlaf, the son of Sitric, the former king of Northumbria, having risen in rebellion against him, and a most fierce war being carried on, Constantiue, king of the Scots, and Eugenius, king of the Cumbrians, and an infinite multitude of other barbarian kings and earls entered into a strict confederacy with the said Anlaf; upon which, all of these, with the nations subject to them, went forth to engage with king Athelstan at Brunford, in Northumbria. When, however, the said king of the English approached with his army, although the barbarian before-named had collected together an infinite multitude of the Danes, Norwegians, Scots, and Picts, either through distrust of conquering, or in accordance with the usual craftiness of his nation, he preferred to resort to stratagem, when protected by the shades of night, rather than engage in open combat.

Accordingly, during the night, he made an attack upon the English, and slew a certain bishop, who the evening before had joined the army of king Athelstan. The cries of the dying being heard at a considerable distance, that king, who was encamped more than a mile from the place of attack, was, together with all his army, awoke from slumber while lying in. their tents beneath the canopy of heaven; and on learning the particulars, they quickly aroused themselves. The dawn was just breaking, when they arrived at the place of slaughter; the king’s troops coming up fresh and prepared for the onset against the barbarians, while they, on the other hand, had been toiling throughout the whole night, and were quite weary and worn out with fatigue. King Althelstan, who was in command of all the men of Wessex, charged the troops of Anlaf, while his chancellor, Turketul, who led on the Londoners and all the Mercians, engaged the forces of Constantine. The discharge of light arms being quickly put an end to, the battle was now fought foot to foot, spear to spear, and shield to shield. Numbers of men were slain, and, amid indiscriminate confusion, the bodies of kings and of common men were strewed upon the ground. After they had now fought for a long time with the most determined courage, and neither side would give way, (so vast was the multitude of the Pagans), the chancellor Turketul taking with him a few of the Londoners, whom he knew to be most distinguished for valour, and a certain captain of the “Wiccii, Singin by name, who was remarkable for his undaunted bravery, (being taller in stature than any of the rest, firm and brawny in bone and muscle, and excelling in strength and robustness any one of the London heroes), flew at their head to the charge against the foe, and, penetrating the hostile ranks, struck them down on the right and on the left.

He had now pierced the ranks of the men of Orkney and the Picts, and, bearing around him a whole forest of darts and javelins, which he had received upon his right trusty cuirass, with his followers had penetrated the dense masses of the Cumbrians and Scots. At last, amid torrents of blood, he reached the king himself, and unhorsed him; and when thus thrown to the ground, made redoubled efforts to take him alive. But the Scots, crowding around their king, used every possible exertion to save him; and, whole multitudes pressing on against a few, they all made Turketul their especial object of attack; who, as he was often in the habit of confessing in after-times, was beginning to repent of the rashness of which he had been guilty.

He was now on the very point of being overwhelmed by the Scots, and their king was just about to be snatched from his grasp, when, at that instant, the captain, Singin, pierced him with his sword. Constantine, the king of tho Scots, being thus slain, his people retreated, and so left the road open to Turketul and his soldiers. The death of Constantine becoming known throughout the whole army, Anlaf took to flight; on which they all followed his example. On this occasion there fell of the Pagans an unheard-of multitude. Turketul frequently made it his boast, that in this hazardous combat he had been preserved by the Lord, and that he esteemed himself most happy end fortunate, in that he had never slain a man, and had not even wounded any one, though at the same time every one may lawfully fight for his country, and especially against the Pagans.