It is narrated from Abu Bakr bin Abdur Rahman (may Allah have mercy on him) that Umm al-Mu'mineen Sayyida Aisha (may Allah be pleased with her) and Umm al-Mu'mineen Sayyida Umm Salama (may Allah be pleased with her) both said: The Messenger of Allah (ﷺ) would be in a state of janabah in the month of Ramadan due to intercourse, not due to a wet dream, and then (in that state) he would also fast that day.
Hadith Referenceالسنن المأثورة / باب صيام من أصبح جنبا / 297
Hadith Takhrijسنن ابی داؤد، الصوم، باب فيمن اصبح جنبا في شهر رمضان، رقم : 2388 وقال الالباني: صحيح