Sayyiduna Ibn Abbas (may Allah be pleased with them both) used to say: The salab (the slain man's gear) is part of the nafl (extra award), and the nafl comes from the khumus (one-fifth). That is what Ibn Abbas (may Allah be pleased with them both) said, whereas the hadiths narrated from the Prophet (peace and blessings be upon him) about the salab indicate that "the salab is taken from the main body of the spoils."
Imam al-Shafi'i (may Allah have mercy on him) said: When something is established from the Prophet (peace and blessings be upon him) (may my father and mother be ransomed for him), it is not permissible to abandon it; and the Prophet (peace and blessings be upon him) made no exception for a small salab or a large one.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12791