Thabit narrates from Sayyiduna Anas (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) had a slave-woman with whom he (peace and blessings be upon him) used to have relations. Because of the insistence of Sayyidah Hafsah (may Allah be pleased with her), he (peace and blessings be upon him) declared that slave-woman forbidden to himself, so Allah Almighty revealed this verse: "O Prophet, why do you forbid what Allah has made lawful for you, seeking the pleasure of your wives?" [Surah al-Tahrim: 1]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الخلع والطلاق / 15076