Sahih Muslim 1750
Sahih Muslim · Book 32: The Book of Jihad and Expeditions · Spoils of War
وَحَدَّثَنَا عَبْدُ الْمَلِكِ بْنُ شُعَيْبِ بْنِ اللَّيْثِ ، حَدَّثَنِي أَبِي ، عَنْ جَدِّي ، قَالَ حَدَّثَنِي عُقَيْلُ، بْنُ خَالِدٍ عَنِ ابْنِ شِهَابٍ ، عَنْ سَالِمٍ ، عَنْ عَبْدِ اللَّهِ ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَدْ كَانَ يُنَفِّلُ بَعْضَ مَنْ يَبْعَثُ مِنَ السَّرَايَا لأَنْفُسِهِمْ خَاصَّةً سِوَى قَسْمِ عَامَّةِ الْجَيْشِ وَالْخُمْسُ فِي ذَلِكَ وَاجِبٌ كُلِّهِ .
It has been narrated on the authority of Abdullah b. 'Umar that the Messenger of Allah (ﷺ) used to give (from the spoils of war) to small troops seat on expeditions something more than the due share of each fighter in a large force. And Khums (one-fifth of the total spoils) was to be reserved (for Allah and His Apostle) in all cases.