Chapter 28: The Book of Oaths
Abu Huraira reported that (Hadrat) Sulaiman had sixty wives. He (one day) said: I will visit each one of them every night, and every one of them will become pregnant and give birth to a male child who will be a horseman and fight in the cause of Allah. But (it so happened) that none of them became pregnant except one, but she gave birth to an incomplete child. Thereupon Allah' s Messenger (ﷺ) said: Had he said Insha' Allah (if God so wills), then every one of them would have given birth to a child who would have been a horseman and fought in the cause of Allah
Sahih Muslim 1654a