Sahih Bukhari Volume 008, Book 078, Hadith Number 634.

Narated By Abu Huraira : Allah's Apostle said, "(The Prophet) Solomon once said, 'Tonight I will sleep with ninety women, each of whom will bring forth a (would-be) cavalier who will fight in Allah's Cause." On this, his companion said to him, "Say: Allah willing!" But he did not say Allah willing. Solomon then slept with all the women, but none of them became pregnant but one woman who later delivered a half-man. By Him in Whose Hand Muhammad's soul is, if he (Solomon) had said, 'Allah willing' (all his wives would have brought forth boys) and they would have fought in Allah's Cause as cavaliers."