It is narrated from Urwah (may Allah have mercy on him) that when Sayyiduna al-Zubayr (may Allah be pleased with him) accepted Islam he was eight years old. Urwah (may Allah have mercy on him) said: Satan spread the rumour that the Messenger of Allah (peace and blessings be upon him) had been seized, so Sayyiduna al-Zubayr (may Allah be pleased with him) came out, being twelve years old, with a sword; whoever saw him and did not recognise him would say: The boy has a sword! Until he came to the Prophet (peace and blessings be upon him). The Messenger of Allah (peace and blessings be upon him) said to him: "O Zubayr, what is the matter with you?" He said: I was told that you had been seized. He (peace and blessings be upon him) said: "And what would you have done?" He said: I would have struck off the head of whoever seized you. So the Messenger of Allah (peace and blessings be upon him) supplicated for him and for his sword, and it was the first sword drawn in Islam.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 13084