Sahih Muslim Book 2, Hadith Number 570.

Chapter : Washing away of the semen from the garment and its scraping.

‘Amr b. Maimun said: I asked Sulaiman b. Yasir whether the semen that gets on to the garment of a person should be washed or not. He replied: ‘Aisha told me: The Messenger of Allah (may peace be upon him) washed the semen, and then went out for prayer in that very garment and I saw the mark of washing on it.