From The Lady of the Linden Tree by Barbara Leonie Picard. (This is one I mentioned earlier)
Sir Merewine of the Hill was accounted among the best of all knights, no matter how one chose to reckon it– whether by skill, or courtesy, good looks or good deeds. He was a truly noble man and was adored by many women, but he politely declined all their attentions.
He had sworn to take as his lady only the most beautiful woman in the world, though he did not yet know who she was.
Nevertheless, he served equally any who had need of him. He was not unkind in his determination to choose the loveliest, only set in his mind.
One day, as he was on his way to a midsummer tourney in the Joyous Valley, he passed by the edge of a wood and heard weeping. Being unable to hear the sound of distress without offering his help, the good knight looked about until he saw a young woman under a linden tree, weeping into her hands.
He approached, asking if there were any way to assist her. When she looked up it took all his skill to carefully conceal his disgust, for she, truly, was the ugliest of women.
The lady explained she had three requests to make of some brave knight, but because of her awful appearance she had been unable to find any willing to help her.
“More shame to them,” said Sir Merewine.
He offered to take on her tasks, and asked what they were, but she would only tell one at a time. The first was a knight Sir Merewine must challenge in her name, in order to bring back his helmet.
Upon meeting the knight, Sir Merewine saw the battle would be hard, but he stood by his word and fought the dark knight until the the larger man fell unconscious under a blow from Sir Merewine.
Having won, Sir Merewine took the fallen knight’s helmet and returned to the lady for the second task.