Sunan Abi Dawud Book 15, Hadith 50
The Prophet (ﷺ) said: The warrior gets his reward, and the one who equips him gets his own reward and that of the warrior.
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) announced an expedition, and I was a very old man and I had no servant. I, therefore, sought a hireling who would serve instead of me, and I would give him his portion. So I found a man. When the time of departure arrived, he came to me and said: I do not know what would be the portions, and how much would be my portion. So offer something (as wages) to me, whether there would be any portion or not. I offered three dinars (as his wages) for him. When some booty arrived, I wanted to offer him his portion. But I remembered the dinars, so I went to the Prophet (ﷺ) and mentioned the matter to him. He said: All I can find for him regarding this expedition of his in this world and the next is three dinars which were offered him.