Sayyida Umm Salama (may Allah be pleased with her)'s brother, 'Amir bin Abu Umayyah, narrates that Sayyida Umm Salama informed him: The Prophet (peace and blessings of Allah be upon him) would be in a state of janabah at the time of true dawn, then he would fast. (The narrator says) So Sayyiduna Abu Hurairah (may Allah be pleased with him) rejected this person's statement.
Hadith Referenceصحیح ابن حبان / كتاب الصوم / 3500
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح: م.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرطهما