Musnad Ahmad 31:216

Yahya ibn Sa'id narrated to us, from Mujalid, who said: Abu al-Wadak narrated to me, from Abu Sa'id, from the Prophet, peace and blessings of Allah be upon him, regarding *al-'azl* (coitus interruptus). He said: "Do whatever seems good to you, for if Allah has decreed a thing, it will be."