Leviticus 25:37

³⁷ το αργυριον σου ου δωσεις αυτω επι τοκω και επι πλεονασμον ου δωσεις αυτω τα βρωματα σου

By Henry MacLagan

Verse 37. For it is unlawful to do good for the sake of reward, either from worldly or selfish motives.