Musannaf Ibn Abi Shayba 1:920

Abu Mu'awiyah narrated to us, from al-A'mash, from Ibrahim, from Hammam, who said: A guest stayed with Aisha, and she ordered a yellow sheet for him. He had a wet dream in it and was shy to send it back while it had the trace of the wet dream on it. So he dipped it in water, then sent it back. Aisha said: "Why did he ruin our garment for us? It would have been sufficient for him to rub it off with his finger. I have often rubbed it off from the garment of the Messenger of Allah, may Allah bless him and grant him peace, with my finger."