Sunan Abi Dawud Book 15, Hadith 49
AbuAyyub heard the Messenger of Allah (ﷺ) say: Capitals will be conquered at your hands, and you will have to raise companies in large armies. A man will be unwilling to join a company, so he will escape from his people and go round the tribes offering himself to them, saying: Whose place may I take in such and such expedition? Whose place may I take in such and such expedition? Beware: That man is a hireling to the last drop of his blood.
The Messenger of Allah (ﷺ) made a brotherhood between two men, one of whom was killed (in Allah's path), and a week or thereabouts later the other died, and we prayed at his funeral). The Messenger of Allah (ﷺ) asked: What did you say? We replied: We prayed for him and said: O Allah, forgive him, and join him to his companion. The Messenger of Allah (ﷺ) said: What about his prayers since the time the other died, and his fasting since the time the other died--the narrator Shu'bah doubted the words, "his fasting--and his deeds since the time the other died. The distance between them is just like the distance between heaven and earth.
The Prophet (ﷺ) said: The warrior gets his reward, and the one who equips him gets his own reward and that of the warrior.