Jami` at-Tirmidhi 779
جامع الترمذي#779SahihAbu Bakr Bin Abdur-Rahman bin Al-Harith bin Hashim said:"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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 8:98