Musnad Ahmad 1153:812

Ibrahim ibn Abi al-Abbas narrated to us, he said: Abu Uways narrated to us, from al-Zuhri, that Urwah ibn al-Zubayr narrated to him, that Aisha, the Mother of the Believers, narrated to him regarding the pledge of allegiance of women: The Messenger of Allah, may Allah bless him and grant him peace, never touched the hand of a woman with his hand at all, except that he would take a pledge from her. When he had taken the pledge from her and she had given it to him, he would say: "Go, for I have accepted your pledge."