Sahih al-Bukhari 293

Musaddad narrated to us, saying: Yahya narrated to us, from Hisham ibn Urwah, who said: My father informed me; Abu Ayyub informed me; Ubayy ibn Kab informed me that he said: “Messenger of Allah, if a man has intercourse with a woman but does not ejaculate?” He said: “He washes what touched the woman of him, then performs ablution and prays.” Abu Abdullah said: “Washing is more precautionary, and that is the later ruling. We included this report only because of their disagreement.”