Musnad Abu Ya'la al-Mawsili 3:327

Zuhayr narrated to us, Jarir narrated to us, from ‘Ata’ ibn al-Sa’ib, from Abu Zabyan, who said: A woman who had committed adultery was brought to ‘Umar, and he ordered that she be stoned. She was led past ‘Ali, and he recognized her, so he let her go. ‘Umar was informed, and it was said to him, "‘Ali took her from our hands and released her." He said, "Call him to me." So he came to him, and he said, "Why did you release her?" He said, "By Allah, you know, O Commander of the Faithful, that the Messenger of Allah (peace and blessings of Allah be upon him) said: 'The pen is lifted from three: from the sleeper until he wakes up, from the child until he reaches puberty, and from the insane person until he recovers.' And this woman is the insane woman of such-and-such tribe, and perhaps the one who committed adultery with her came to her while she was in her state of affliction."