Abu Dawud Book 1, Hadith Number 215.
Chapter : Bathing is obligatory after sexual intercourse without seminal emmision.
Narated By Ubayy b. Ka’b : The verdict that water (bath) is necessary when there is emission given by the people (in the early days of Islam) was due to the concession granted by the Apostle of Allah in the beginning of Islam. He then commanded to take a bath (in such a case).
Abu Dawud said: By Abu GhassÃ¤n is meant Muhammad b. Mutarrif.