Musnad Ahmad 1153:2341

Sa'd ibn Ibrahim narrated to us, he said: My father narrated to us, from Muhammad ibn Ishaq, he said: Thawr ibn Yazid al-Kila'i—and he was trustworthy—narrated to me, from Muhammad ibn 'Ubayd ibn Abi Salih al-Makki, he said: I performed Hajj with 'Adi ibn 'Adi al-Kindi, and he sent me to Safiyyah bint Shaybah ibn 'Uthman, the keeper of the Ka'bah, to ask her about things she had heard from 'Aishah, the wife of the Prophet, may Allah bless him and grant him peace, from the Messenger of Allah, may Allah bless him and grant him peace. Among what she narrated to me was that she heard 'Aishah say: I heard the Messenger of Allah, may Allah bless him and grant him peace, say: "There is no divorce and no manumission under coercion (ighlaq)."