Musnad Ahmad 1153:636

Muhammad ibn Ja'far narrated to us, he said: Shu'bah narrated to us, from Isma'il ibn Abi Khalid, he said: I heard al-Sha'bi narrating from Masruq, from 'Aishah, that she said: "The Messenger of Allah, peace and blessings of Allah be upon him, gave his wives the choice. Was that considered a divorce?"