Sayyidah Aishah and Umm Salamah (may Allah be pleased with them both), the wives of the Prophet (peace and blessings be upon him), say that if he (peace and blessings be upon him) woke up in the morning in a state of janabah from intercourse, he (peace and blessings be upon him) would fast. [Sahih. Recorded by Malik]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7991