Musnad Ahmad 7:5

Abu Usamah narrated to us, Hisham informed us, from his father, from Abdullah ibn al-Zubayr, who said: On the day of the Trench, I and Umar ibn Abi Salamah were in the fortress in which the women of the Messenger of Allah (peace and blessings of Allah be upon him) were, the fortress of Hassan. He would lift me up and I would lift him up. When he lifted me up, I would recognize my father when he passed by toward Banu Qurayzah, and he was fighting alongside the Messenger of Allah (peace and blessings of Allah be upon him) on the day of the Trench. He [the Prophet] had said: "Who will go to Banu Qurayzah and fight them?" When he [my father] returned, I said to him: "O my father, by Allah, I used to recognize you when you passed by going to Banu Qurayzah." He said: "O my son, by Allah, the Messenger of Allah (peace and blessings of Allah be upon him) would gather both of his parents for me, sacrificing them for me, saying: 'May my father and mother be sacrificed for you.'"