Erasmus, Adagia 33:
Socrates in the Axiochus of Plato, says to the sophist Prodicus that this little verse of the comic Epicharmus was always in his mouth: Ἡ δὲ χεὶρ τὴν χεῖρα κνίζει, δός τι καὶ λάβοις τι, that is, one hand wipes the other, give something and get something, obviously reproaching in a humorous way the greed of a man who taught no one for free, and from whom he affirmed that he himself had learned what he was about to speak not for free, but by paying a fee. This idea was worthy then of a Sicilian, then of a ‘cunning poet.’ For thus Cicero labels him. It does, however, advise us that no one can be found who would wish to do someone a service without wishing that the other would repay the favor in turn: rather, duty is called forth by duty, favors called forth by favors. The same adage is expressed this way: Χεὶρ χεῖρα νίπτει, that is, one hand washes the other. Either metaphor has the same sense, for it is a kind of shared benefit when one hand either wipes or washes the other. There is a distich of this sort which was fashionable among the Greeks: Ἀνὴρ γὰρ ἄνδρα καὶ πόλις σῴζει πόλιν. Χεὶρ χεῖρα νίπτει, δάκτυλος τε δάκτυλον, that is, one man saves another, one citiy saves the other; the hand washes the hand and the finger cleans the finger. Seneca uses this phrase in that ridiculous little book about the death of Claudius.
MANVS MANVM FRICAT
Socrates in Axiocho Platonis ait Prodico sophistae hunc Epicharmi comici versiculum semper in ore fuisse: Ἡ δὲ χεὶρ τὴν χεῖρα κνίζει, δός τι καὶ λάβοις τι, id est Affricat manum manus, da quiddam et aliquid accipe, videlicet hominis quaestum facete taxans, qui neminem gratis doceret et a quo se quoque quae tum dicturus esset, didicisse affirmabat, at ne id quidem gratuito, imo numerata mercede. Sententia digna tum homine Siculo tum ‘vafro poeta’; sic enim illum appellat Cicero. Monet autem neminem ferme mortalium inueniri, qui velit in quempiam beneficium collocare, a quo non speret aliquid emolumenti vicissim ad se rediturum, sed officium inuitari officio, beneficium beneficio prouocari. Idem adagium effertur et hoc pacto: Χεὶρ χεῖρα νίπτει, id est Manum manus lauat. Idem pollet vtraque metaphora. Nam mutua commoditas est, quoties vel fricat vel abluit manus manum. Circunfertur inter Graecanicas sententias huiusmodi distichon: Ἀνὴρ γὰρ ἄνδρα καὶ πόλις σῴζει πόλιν.