Matthew 6:22

Ὁ λύχνος τοῦ σώματός ἐστιν ὁ ὀφθαλμός· ἐὰν οὖν ὁ ὀφθαλμός σου ἁπλοῦς ᾖ, ὅλον τὸ σῶμά σου φωτεινὸν ἔσται·

The light of the body is the eye. If then your eye be clear, your whole body will be full of light.