Abu Ayyub Al-Ansari narrated that:
The Prophet said: "The five daily prayers, from one Friday to the next, and fulfilling the trust are all expiation for whatever (sins) come between them." I said: "What is fulfilling the trust?" He said: Having a bath to cleanse oneself from sexual impurity, for under every hair there is the state of sexual impurity."
English reference: Vol. 1, Book 1, Hadith 598
Arabic reference: Book 1, Hadith 641