Al-Baqarah - 2:207

وَمِنَ النَّاسِ مَن يَشْرِي نَفْسَهُ ابْتِغَاء مَرْضَاتِ اللّهِ وَاللّهُ رَؤُوفٌ بِالْعِبَادِ
[2:207]
And among men is he who sells himself to seek the pleasure of Allah; and Allah is Affectionate to the servants.
And there is the type of man who gives his life to earn the pleasure of Allah: And Allah is full of kindness to (His) devotees.
And of mankind is he who would sell himself, seeking the pleasure of Allah; and Allah hath compassion on (His) bondmen.