سنن أبي داود

Narrated AbuAyyub al-Ansari:

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.