Musnad Ahmad 479:1

Muhammad ibn Bishr narrated to us, he said: Muhammad ibn ‘Amr narrated to us, he said: Abu Kathir, the freed slave of the Laythis, narrated to me, from Muhammad ibn ‘Abdullah ibn Jahsh, that a man came to the Prophet, may God bless him and grant him peace, and said: "O Messenger of God, what is for me if I am killed in the way of God?" He said: "Paradise." Then, when he turned away, he said: "Except for debt; Gabriel, peace be upon him, whispered it to me just now."