From Sahih Bukhari (Hadith 231):
Narrated `Amr bin Maimun:I heard Sulaiman bin Yasar talking about the clothes soiled with semen. He said that `Aisha had said, "I used to wash it off the clothes of Allah's Messenger (ﷺ) and he would go for the prayers while water spots were still visible on them
Reference: Bukhari 231