The strength of thirty men...
Anas bin Malik said, “The Prophet صلى الله عليه و سلم used to visit all his wives in a round, during the day and night and they were eleven in number.” I asked Anas, "Had the Prophet the strength for it?" Anas replied;
"We used to say that the Prophet was given the strength of thirty (men)."
[Sahih Al Bukhari, Book of Bathing, Hadith No: 269]