If any of you lack the means to marry free believing women, he may marry one of the believing maids under your control. God is well aware of your faith. You are from one another. Marry them with the permission of their guardians, and give them their recompense fairly—to be protected—neither committing adultery, nor taking secret lovers. When they are married, if they commit adultery, their punishment shall be half that of free women. That is for those among you who fear falling into decadence. But to practice self-restraint is better for you. God is Most Forgiving, Most Merciful.

The Holy Quran · An-Nisaa (The Women) · 4:25