Sufyaan narrated to us from [Muhammad] ibn al-Munkadir who said that he heard Jaabir ibn ‘Abdullaah ( May Allah be pleased with him) say,
“The Messenger of Allah exhorted the people on the day the Battle of al-Khandaq took place to fight, and az-Zubayr said, ‘I am ready to participate.’ Then he exhorted them again and az-Zubayr said, ‘I am ready to participate.’ Then he exhorted them again and az-Zubayr said, ‘I am ready to participate.’ The then said, ‘Every prophet has a helper, and my helper is az-Zubayr.”‘
(Musnad Ahmad, Vol. 3, p. 307. The isnaad of this hadeeth is Saheeh according to the conditions set by al-Bukhaaree and Muslim.)
Az-Zubayr ibn al-‘Awwaam was a cousin of the Prophet ( peace be on him): He embraced Islam when he was fifteen years old and participated in all the battles of Islam. He was one of the ten companions to whom the prophet ( peace be on him) gave the good news of the reward of Paradise during their lifetimes.
Source:
Thulaathiyyaat Musnad Ahmad ibn Hanbal (may Allah have mercy on him)
Reports of Imaam Ahmad that have only three narrators between him and the Prophet, peace, and blessings be upon him.
Shaykh Muhammad ibn Ahmad ibn Saalim as–Saffaareenee al–Hanbalee ~(1114 –1188 AH)