Musnad Ahmad 763:2

Khalaf ibn al-Walid narrated to us, 'Abbad ibn 'Abbad narrated to us, Muhammad ibn 'Amr narrated to us, from Abu Kathir, the freed slave of the Hudhaylis, from Muhammad ibn 'Abdullah ibn Jahsh, from his father, who said: A man came to the Prophet, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, what is for me if I fight in the way of Allah until I am killed?" He said: "Paradise." He said: When he turned away, the Messenger of Allah, peace and blessings of Allah be upon him, said: "Except for debt; Jibril, peace be upon him, whispered it to me."