מדרש על כתובות 135:20

"lest there be in your heart a thing belial": From here R. Yehoshua b. Karchah was wont to say: Averting one's eyes from charity is tantamount to serving idols, it being written here "belial," and elsewhere (re idolatry) "belial." Just as there, idolatry is meant, here, too, idolatry.