Narrated Abdullah ibn Umar: The Messenger of Allah ﷺ used to give to some of the detachments he sent out (something extra) for themselves in particular apart from the division made to the whole army. The fifth is necessary in all that.
Hadith Referenceسنن ابي داود / كتاب الجهاد / 2746
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح بخاري (3135) صحيح مسلم (1750)