Musnad Ahmad 25:1530

Isma'il narrated to us, Ayyub narrated to us, from 'Abdullah ibn Sa'id ibn Jubayr, from his father, from Ibn 'Abbas, who said: I spent the night at the house of my maternal aunt, Maymunah. The Messenger of Allah (peace and blessings of Allah be upon him) stood up to pray during the night, so I stood up to pray with him. I stood on his left side, so he did this to me; he took hold of my head and placed me on his right side.