Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with them both) said: "In the year of Khaybar the Messenger of Allah (peace and blessings be upon him) allotted four shares: a share for al-Zubayr, a share on account of kinship, a share for his mother, and a share for his horse."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13848