Sahih Bukhari Volume 007, Book 062, Hadith Number 169.
Narrated By Abu Huraira : (The Prophet) Solomon son of (the Prophet) David said, "Tonight I will go round (i.e. have sexual relations with) one hundred women (my wives) everyone of whom will deliver a male child who will fight in Allah's Cause." On that an Angel said to him, "Say: 'If Allah will.' " But Solomon did not say it and forgot to say it. Then he had sexual relations with them but none of them delivered any child except one who delivered a half person. The Prophet said, "If Solomon had said: 'If Allah will,' Allah would have fulfilled his (above) desire and that saying would have made him more hopeful."