Musnad Ahmad 27:820

Rawh ibn ‘Ubadah narrated to us, Ibn Jurayj narrated to us, Abu al-Zubayr informed me that he heard ‘Abd al-Rahman ibn Ayman asking Ibn ‘Umar, while Abu al-Zubayr was listening. Ibn ‘Umar said: The Prophet, peace and blessings of Allah be upon him, recited: "O Prophet, when you divorce women, divorce them at the beginning of their waiting period."