Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 371
Narated By N/A : Hammam b. al-Harith reported, he had a sexual dream when he was staying with 'Aisha. The slave-girl of 'Aisha saw him when he was washing the mak of defilement, or he was washing his clothe. She informed 'Aisha who said: He witnessed me rubbing off the semen from the clothe of the Apostle of Allah (pbuh).
Abu Dawud said: Al-A'mash narrated it as narrated by al-Hakam.