Khuthaym bin Irak (may Allah have mercy on him) said: I heard my father narrate that Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrated that the Prophet (peace and blessings be upon him) said: "There is no zakah on a Muslim's slave or horse."
That Irak bin Malik (may Allah have mercy on him) heard from Sayyiduna Abu Hurayrah (may Allah be pleased with him) is established. This is authentic; there is no doubt in it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7400