{ And among the people there are those who sell themselves seeking after the good pleasures of Allah; and Allah is compassionate to the servants. Oh you who have believed! Enter completely into peace and do not follow the steps of Satan; indeed he is a clear enemy to you } Al-baqara 207-208

He (may His praise be exalted) means: Among the people there are those who sell themselves for what Allah has promised to the mujahideen for His sake, and for which He has bought them, according to His word: { Indeed Allah has bought, from the Believers, their lives and their wealth, so that Jannah may be theirs } [Al-tawba 111].