Abu Bakr bin 'Abdur Rahman أبو بكر بن عبد الرحمن بن الحارث بن هشام · The Book on Fasting

"Aishah and Umm Salamah, the wives of the Prophet informed me that the Prophet would find that it was Fajr while he was Junub from (relations with) his wives, then he would perform Ghusl and fast."