Musnad Ahmad 31:838

Abu al-Yaman narrated to us, Shu'ayb informed us, from al-Zuhri, 'Abdullah ibn Muhayriz al-Jumahi informed me, that Abu Sa'id al-Khudri informed him, that while he was sitting with the Prophet, may Allah bless him and grant him peace, a man from the Ansar came and said: "O Messenger of Allah, we capture female captives and we desire their price (or we desire to avoid pregnancy), so what is your opinion on *al-'azl* (coitus interruptus)?" The Prophet, may Allah bless him and grant him peace, said: "And do you really do that? It does not matter if you do not do that, for there is no soul that Allah has decreed to come forth, but it will come forth."