Musnad Ahmad 5:792

Abu Sa’id narrated to us, Hammad ibn Salamah narrated to us, from ‘Ata’ ibn al-Sa’ib, from Abu Zabyan, that ‘Ali, may Allah be pleased with him, said to ‘Umar, may Allah be pleased with him: "O Commander of the Faithful, have you not heard the Messenger of Allah, may Allah bless him and grant him peace, say: 'The pen is lifted from three: from the sleeper until he wakes up, from the child until he grows up, and from the afflicted [mentally ill] until he regains his reason'?"