Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 214
Narated By Ubayy b. Ka'b : The Apostle of Allah (may peace be upon him) made a concession in the early days of Islam on account of the paucity of clothes that one should not take a bath if one has sexual intercourse (and has no seminal emission). But later on he commanded to take a bath in such a case and prohibited its omission.