Sahih al-Bukhari 1931
Sahih al-Bukhari · Book 30: Fasting · Taking a bath by a person observing Saum (fast)
Narrated Abu Bakr bin `Abdur-Rahman:
حَدَّثَنَا إِسْمَاعِيلُ ، قَالَ حَدَّثَنِي مَالِكٌ ، عَنْ سُمَىٍّ، مَوْلَى أَبِي بَكْرِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ الْحَارِثِ بْنِ هِشَامِ بْنِ الْمُغِيرَةِ أَنَّهُ سَمِعَ أَبَا بَكْرِ بْنَ عَبْدِ الرَّحْمَنِ ، كُنْتُ أَنَا وَأَبِي،، فَذَهَبْتُ مَعَهُ، حَتَّى دَخَلْنَا عَلَى عَائِشَةَ ـ رضى الله عنها ـ قَالَتْ أَشْهَدُ عَلَى رَسُولِ اللَّهِ صلى الله عليه وسلم إِنْ كَانَ لَيُصْبِحُ جُنُبًا مِنْ جِمَاعٍ غَيْرِ احْتِلاَمٍ، ثُمَّ يَصُومُهُ. ثُمَّ دَخَلْنَا عَلَى أُمِّ سَلَمَةَ ، فَقَالَتْ مِثْلَ ذَلِكَ .
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.