Sunan an-Nasa'i, Volume 4, Book 26, Hadith 3220 (DarusSalam) ⓘ
Narrated Abu Hurairah: It was narrated from Abu Hurairah that the Messenger of Allah said: "There are three who are promised the help of Allah: The Mukatab who wants to buy his freedom, the one who gets married seeking to keep himself chaste, and the Mujahid who fights in the cause of Allah." *Mukatab: the slave who has made a contract of manumission.
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنْ مُحَمَّدِ بْنِ عَجْلاَنَ، عَنْ سَعِيدٍ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " ثَلاَثَةٌ حَقٌّ عَلَى اللَّهِ عَزَّ وَجَلَّ عَوْنُهُمُ الْمُكَاتَبُ الَّذِي يُرِيدُ الأَدَاءَ وَالنَّاكِحُ الَّذِي يُرِيدُ الْعَفَافَ وَالْمُجَاهِدُ فِي سَبِيلِ اللَّهِ " .
also referenced under: Hadith 3218 (Reference) & Book 26, Hadith 23 (In-Book)