(25) باب اغْتِسَالِ الصَّائِمِ
Narrated Abu Bakr bin `Abdur-Rahman:
My father and I went to `Aisha and she said, "I testify that Allah's Messenger (ﷺ) at times used to get up in the morning in a state of Janaba from sexual intercourse, not from a wet dream and then he would fast that day." Then he went to Um Salama and she also narrated a similar thing.
Reference: Sahih al-Bukhari 1931, 1932
In-book reference: Book 30, Hadith 39
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 31, Hadith 153