Musnad Abu Ya'la al-Mawsili 115:100

Ubayd Allah ibn Umar al-Qawariri narrated to us, Mu'adh narrated to us, my father narrated to us, from Qatadah, from Anas: That the Prophet of Allah, peace and blessings of Allah be upon him, used to go around to his wives during the hour of the night and the day, and they were eleven. He (the narrator) said: I said to Anas, "Was he capable of that?" He said, "We used to say that he was given the strength of thirty."