Musannaf Ibn Abi Shayba 1:917

Abu Bakr narrated to us, he said: Hushaym narrated to us, from Mughirah, from Ibrahim, from al-Aswad, from ‘Aishah, she said: I have seen myself finding it on the garment of the Messenger of Allah, may Allah bless him and grant him peace, and I would scrape it off from it—meaning the semen.