Musnad Ahmad 913:1

Yahya ibn Sa'id narrated to us, Hisham ibn 'Urwah informed us, my father informed me, Abu Ayyub informed us, that Ubayy narrated to him, he said: I asked the Messenger of Allah, may Allah bless him and grant him peace, I said: A man has intercourse with his wife, but does not ejaculate? He said: "He shall wash what touched the woman from him, perform ablution, and pray."