Musnad Ahmad 5:392

Bahz and 'Affan narrated to us, they said: Hammam narrated to us, from Qatadah, from al-Hasan, from 'Ali, that the Prophet, peace and blessings of Allah be upon him, said: "The pen is lifted from three: from the sleeper until he wakes up, and from the mentally deficient—or he said: the insane—until he regains his reason, and from the child until he reaches puberty."