Musnad Ahmad 1153:1186

Yahya ibn Adam narrated to us, Ibn al-Mubarak narrated to us, from Ma'mar, from al-Zuhri, from 'Urwah, from 'Aishah, she said: "The hand of the Messenger of Allah, peace and blessings of Allah be upon him, never touched the hand of a woman in an oath of allegiance (bay'ah) at all."