Musnad Ahmad 1007:26

Yazid ibn Harun narrated to us, Yahya ibn Sa'id informed us, that Sa'id ibn Abi Sa'id al-Maqburi informed him, that Abdullah ibn Abi Qatadah informed him, that his father used to narrate that a man asked the Prophet, may Allah bless him and grant him peace, and said: "O Messenger of Allah, do you see if I am killed in the way of Allah, patient, seeking reward, advancing, not retreating, will Allah expiate my sins for me?" The Messenger of Allah, may Allah bless him and grant him peace, said: "If you are killed in the way of Allah, patient, seeking reward, advancing, not retreating, Allah will expiate your sins for you." Then the Messenger of Allah, may Allah bless him and grant him peace, remained for as long as Allah willed, then the man asked him and said: "O Messenger of Allah, if I am killed in the way of Allah, advancing, not retreating, will Allah expiate my sins for me?" The Messenger of Allah, may Allah bless him and grant him peace, said: "If you are killed in the way of Allah, advancing, not retreating, Allah will expiate your sins for you, except for debt. That is what Jibril said to me."