Musnad Ahmad 1153:2388

I found in my father’s book: ‘Amir ibn Salih narrated to us, he said: Malik ibn Anas narrated to me, from Ibn Shihab, from ‘Urwah, from ‘Amrah, from ‘Aishah, that she said: "When the Messenger of Allah, peace and blessings of Allah be upon him, was in I’tikaf, he would not leave the mosque except for human necessity."