Musannaf Ibn Abi Shayba 18:811

Abu Bakr narrated to us, he said: Abu Usama narrated to us, from Hisham, from al-Hasan, that he said regarding the insane person, the one overcome in his intellect, the mentally deficient, and the one who is afflicted once or twice a month: If that state leaves him, and he fasts, prays, possesses intellect, and acquires something, then he is responsible for it.