Musnad Ahmad 31:468

Bahz narrated to us, Shu'bah narrated to us, he said: Anas ibn Sirin narrated to me, from his brother Ma'bad ibn Sirin, from Abu Sa'id al-Khudri—Shu'bah said: I said to him, "Did you hear it from Abu Sa'id?" He said, "Yes"—from the Prophet, peace and blessings of Allah be upon him, regarding *al-'azl* (coitus interruptus), he said: "It does not matter if you do not do that; for it is only the decree."