Yahya bin Abbad bin Abdullah bin al-Zubayr narrates from his grandfather (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) allotted four shares to al-Zubayr bin al-Awwam (may Allah be pleased with him) on the day of Khaybar: one share for him, one for his relative, Safiyyah bint Abd al-Muttalib (may Allah be pleased with her), al-Zubayr's mother, and two shares for the horse.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17965