Sahih Muslim Book 15, Hadith Number 4067.

Abu Huraira reported Allah’s Prophet (may peace be upon him) as saying that Sulaiman b. Dawud, the Apostle of Allah, observed: I will have an intercourse with seventy wives during the night; all of them will give birth to a male child who will fight in the cause of Allah. His companion or the ang I said to him: Say, “If God wills.” But he (Hadrat Sulaimin) did not say so, and he forgot it. And none of his wives gave birth to a child, but one who gave birth to a premature child. Allah’s Messenger (may peace be upon him) said: Had he said Insha’ Allah (if God so will), he would not have failed and his desire would have been materialised.