Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 366
Narated By Umm Habibah : Mu'awiyah ibn AbuSufyan asked his sister Umm Habibah, the wife of the Prophet (pbuh): Would the apostle of Allah (pbuh) pray in the clothe in which he had an intercourse? She said: Yes, when he would not see any impurity in it.