Sayyiduna Ubadah bin al-Samit (may Allah be pleased with him) said: I taught the people of al-Suffah writing and the recitation of the Qur'an. A man among them gave me a bow as a gift. I said: It is not wealth, and I will shoot with it in the cause of Allah. I will certainly go to the Messenger of Allah (peace and blessings be upon him) and ask him (peace and blessings be upon him) about it. I came to him (peace and blessings be upon him) and said: O Messenger of Allah (peace and blessings be upon him)! A man has given me a bow in return for writing and the Qur'an; it is not wealth, and I will shoot with it in the cause of Allah? He (peace and blessings be upon him) said: "If you would like to be collared with a collar of fire, then accept it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الإجارة / 11681