Sayyiduna Ali bin Abi Talib (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "From the spoils, a slave is given only low-value goods, and his grant of protection is valid when he gives people protection."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18172