Musnad Ahmad 1007:110

Yazid ibn Harun narrated to us, Yahya ibn Sa'id informed us, from Sa'id al-Maqburi, from 'Abdullah ibn Abi Qatadah, from his father, who said: A man came to the Prophet, may Allah bless him and grant him peace, and said: "O Messenger of Allah, if I am killed in the way of Allah, patient and seeking reward, advancing and 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 and seeking reward, advancing and not retreating, Allah will expiate your sins for you." Then the man remained for as long as Allah willed, then he said: "O Messenger of Allah, if I am killed in the way of Allah, 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 and seeking reward, advancing and not retreating, Allah will expiate your sins for you, except for debt. That is what Jibril told me."