οὐδὲν ἀπολείπειν προθυμίας

From LSJ

οἱ βάρβαροι γὰρ ἄνδρας ἡγοῦνται μόνους τοὺς πλεῖστα δυναμένους καταφαγεῖν καὶ πιεῖν → for great feeders and heavy drinkers are alone esteemed as men by the barbarians

Source

Greek > English (Woodhouse)

not to let one's zeal cool