Musnad Ahmad 1153:1080

Yazid narrated to us, he said: 'Amr ibn Maymun informed us, he said: Sulayman ibn Yasar narrated to us, he said: 'Aisha informed me: "That she used to wash the semen from the garment of the Messenger of Allah, may Allah bless him and grant him peace, then he would go out and pray, while I was looking at the spots on his garment from the effect of the washing."