Bede's Ecclesiastical History of England, ed. by A.M. Sellar, , at sacred-texts.com
ABOUT the same time, another traveller, a Briton, as is reported, happened to pass by the same place, where the aforesaid battle was fought. Observing one particular spot of ground greener and more beautiful than any other part of the field, he had the wisdom to infer that the cause of the unusual greenness in that place must be that some person of greater holiness than any other in the army had been killed there. Ide therefore took along with him some of the dust of that piece of ground, tying it up in a linen cloth, supposing, as was indeed the case, that it would be of use for curing sick people, and proceeding on his journey, came in the evening to a certain village, and entered a house where the villagers were feasting at supper. Being received by the owners of the house, he sat down with them at the entertainment, hanging the cloth, with the dust which he had carried in it, on a post in the wall. They sat long at supper and drank deep. Now there was a great fire in the middle of the room, and it happened that the sparks flew up and caught the roof of the house, which being made of wattles and thatch, was suddenly wrapped in flames; the guests ran out in panic and confusion, but they were not able to save the burning house, which was rapidly being destroyed. Wherefore the house was burnt down, and only that post on which the dust hung in the linen cloth remained safe and untouched by the fire. When they beheld this miracle, they were all amazed, and inquiring into it diligently, learned that the dust had been taken from the place where the blood of King Oswald had been shed. These wonderful works being made known and reported abroad, many began daily to resort to that place, and received the blessing of health for themselves and their friends.