Clement of Alexandria, Miscellanies 1.7.38
For the teaching of godliness is a gift, and faith itself is grace. By doing the will of God we come to know the will.
Greek
δωρεὰ γὰρ ἡ διδασκαλία τῆς θεοσεβείας, χάρις δὲ ἡ πίστις. ποιοῦντες γὰρ τὸ θέλημα τοῦ θεοῦ τὸ θέλημα γινώσκομεν.