Chapter 56: Fighting for the Cause of Allah (Jihaad)
Narrated Abu Huraira: Allah' s Messenger (ﷺ) said, "Once Solomon, son of David said, '(By Allah)
Tonight I will have sexual intercourse with one hundred (or
ninety-nine) women each of whom will give birth to a knight who will
fight in Allah' s Cause.' On that a (i. e. if Allah wills) but he did
not say, 'Allah willing.' Therefore only one of those women conceived
and gave birth to a half-man. By Him in Whose Hands Muhammad' s life
is, if he had said, "Allah willing', (he would have begotten sons) all
of whom would have been knights striving in Allah' s Cause."
Sahih al-Bukhari 2819