كتاب الجهاد والسير
Read the English translation first, with the original Arabic directly underneath.
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."
قَالَ سُلَيْمَانُ بْنُ دَاوُدَ ـ عَلَيْهِمَا السَّلاَمُ ـ لأَطُوفَنَّ اللَّيْلَةَ عَلَى مِائَةِ امْرَأَةٍ ـ أَوْ تِسْعٍ وَتِسْعِينَ ـ كُلُّهُنَّ يَأْتِي بِفَارِسٍ يُجَاهِدُ فِي سَبِيلِ اللَّهِ، فَقَالَ لَهُ صَاحِبُهُ إِنْ شَاءَ اللَّهُ. فَلَمْ يَقُلْ إِنْ شَاءَ اللَّهُ. فَلَمْ يَحْمِلْ مِنْهُنَّ إِلاَّ امْرَأَةٌ وَاحِدَةٌ، جَاءَتْ بِشِقِّ رَجُلٍ، وَالَّذِي نَفْسُ مُحَمَّدٍ بِيَدِهِ، لَوْ قَالَ إِنْ شَاءَ اللَّهُ، لَجَاهَدُوا فِي سَبِيلِ اللَّهِ فُرْسَانًا أَجْمَعُونَ