It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) assigned three shares for the man and his horse: one share for him and two for his horse.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12867