From Sahih Muslim (Hadith 2592):
Abu Bakr b. 'Abd al-Rahman b. al-Harith b. Hisham reported on the authority of 'A'isha and Umm Salama, the wives of the Messenger of Allah (ﷺ):The Messenger of Allah (ﷺ) at times got up in the morning in a state of junub on account of having a sexual intercourse (with his wives during night) but not due to sexual dreams in the month of Ramadan, and would observe fast
Reference: Muslim 2592