Musnad Ahmad 1153:1648

Yahya narrated to us, from Isma'il, who said: 'Amir informed me, from Masruq, who said: I asked 'Aisha about the *khiyara* (the choice given to a wife). She said: "The Messenger of Allah (peace and blessings of Allah be upon him) gave us the choice; was that a divorce?"