Musnad Ahmad 25:6

Hushaym narrated to us, Abu Bishr informed us, from Sa’id ibn Jubayr, from Ibn Abbas, who said: "I spent a night at the house of my maternal aunt, Maymunah bint al-Harith, and the Messenger of Allah (peace and blessings of Allah be upon him) was with her on her night. He stood to pray during the night, so I stood to his left to pray with his prayer. He said: So he took hold of a lock of hair that I had—or my head—until he placed me to his right."