A man came to the Prophet (PBUH) and said, O Messenger of Allah, if I am killed in the cause of Allah, patiently and having the best expectations of Allah, facing up and not backing off (advancing and not retreating); will Allah expiate my sins? So the Messenger of Allah (PBUH) replied: Yes. After the man turned away, the Messenger of Allah (PBUH) called or commanded the man to be called, so he was called. The Messenger of Allah (PBUH) said to him: What did you say?The man repeated his question, so the Prophet (PBUH) said: Yes, except debt, Gabriel told me so.

A funeral was brought to the Prophet (PBUH) to pray over it. He asked: Is he in debt? They said: No. So he prayed over it. Then another funeral was brought to him. He asked: Is he in debt? They said: Yes. He said: Pray over your companion. Abu Qatadah said: I'll pay off his debt, O Messenger of Allah. So the Prophet (PBUH) prayed over it.

Getting killed in the cause of Allah expiates everything except for debt.