As Lancelot went his way through the forest he met with many hermits who dwelled therein, and had adventure with the Knight who stole his horse and his helm, and got them back again. And he learned from one of the hermits that Sir Galahad was his son, and that it was he who at the Feast of Pentecost had sat in the Siege Perilous, which it was ordained by Merlin that none should sit in save the best Knight in the world. All that night Sir Lancelot abode with the hermit and laid him to rest, a hair shirt always on his body, and it pricked him sorely, but he bore it meekly and suffered the pain. When the day dawned he bade the hermit farewell. As he rode he came to a fair plain, in which was a great castle set about with tents and pavilions of divers hues. Here were full five hundred Knights riding on horseback, and those near the castle were mounted on black horses with black trappings, and they that were without were on white horses and their trappings white. And the two sides fought together, and Sir Lancelot looked on.
At last it seemed to him that the black Knights nearest the castle fared the worst, so, as he ever took the part of the weaker, he rode to their help and smote many of the white Knights to the earth and did marvellous deeds of arms. But always the white Knights held round Sir Lancelot to tire him out. And as no man may endure for ever, in the end Sir Lancelot waxed so faint of fighting that his arms would not lift themselves to deal a stroke; then they took him, and led him away into the forest and made him alight from his horse and rest, and when he was taken the fellowship of the castle
were overcome for want of him. 'Never ere now was I at tournament or jousts but I had the best,' moaned Sir Lancelot to himself, as soon as the Knights had left him and he was alone. 'But now am I shamed, and I am persuaded that I am more sinful than ever I was.' Sorrowfully he rode on till he passed a chapel, where stood a nun, who called to him and asked him his name and what he was seeking.
So he told her who he was, and what had befallen him at the tournament, and the vision that had come to him in his sleep. 'Ah, Lancelot,' said she, 'as long as you were a Knight of earthly knighthood you were the most wonderful man in the world and the most adventurous. But now, since you are set among Knights of heavenly adventures, if you were worsted at that tournament it is no marvel. For the tournament was meant for a sign, and the earthly Knights were they who were clothed in black in token of the sins of which they were not yet purged. And the white Knights were they who had chosen the way of holiness, and in them the quest has already begun. Thus you beheld both the sinners and the good men, and when you saw the sinners overcome you went to their help, as they were your fellows in boasting and pride of the world, and all that must be left in that quest. And that caused your misadventure. Now that I have warned you of your vain-glory and your pride, beware of everlasting pain, for of all earthly Knights I have pity of you, for I know well that among earthly sinful Knights you are without peer.'