Musnad Ahmad 1153:149

Abu Mu’awiyah narrated to us, Al-A’mash narrated to us, from Ibrahim, from Hammam, who said: A guest stayed with Aisha, so she ordered a yellow sheet of hers for him. He slept in it and had a wet dream. He felt shy to send it back while the trace of the wet dream was on it. He said: So he dipped it in water, then sent it back. Aisha said: "Why did he spoil our garment for us? It would have sufficed him to rub it with his fingers. I have indeed rubbed it from the garment of the Messenger of Allah, may Allah bless him and grant him peace, with my fingers."