Ubaydullah bin Miqsam (may Allah have mercy on him) said: I asked Malik bin Aws (may Allah be pleased with him) about the spoils (nafl), and he said: I rode horses in the Jahiliyyah, and I found people taking (extra awards) only from the khumus.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12813