αἱ σπονδαὶ ἐνιαυτὸν ἔσονται

From LSJ

Τὸ μανθάνειν δ' ἥδιστον εὖ λέγοντος, εἰ κέρδος λέγοι → It is the sweetest thing to learn from one speaking well, if they speak profitably

Sophocles, Antigone, 1031-2