Muhammad bin Sirin (may Allah have mercy on him) relates that Sayyiduna al-Bara' bin Malik (may Allah be pleased with him), the brother of Sayyiduna Anas bin Malik (may Allah be pleased with him), fought the Marzuban of al-Zarah in single combat, killed him and then took his spoils (salab), and his spoils reached thirty thousand. When this reached Sayyiduna Umar bin al-Khattab (may Allah be pleased with him), he said to Sayyiduna Abu Talhah (may Allah be pleased with him): "We used not to take a fifth from the spoils of the slain, but the spoils of al-Bara' have reached a great amount, so I think we should take a fifth of it."
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1169