Book 24, Hadith 2

It was narrated from Abu Sa’eed Al-Khudri that the Prophet (ﷺ) said:“The one who fights in the cause of Allah has a guarantee from Allah. Either He will raise him to His forgiveness and mercy, or He will send him back with reward and spoils of war. The likeness of the one who fights in the cause of Allah is that of one who fasts and prays at night without ceasing, until he returns.”