Plato, Laws 665e

ᾠδὰς μεστός, καὶ χαίρει τε ἧττον πράττων τοῦτο καὶ ἀνάγκης γιγνομένης αἰσχύνοιτʼ ἂν μᾶλλον, ὅσῳ πρεσβύτερος καὶ σωφρονέστερος γίγνεται, τόσῳ μᾶλλον. ἆρʼ οὐχ οὕτως; οὕτω μὲν οὖν. οὐκοῦν ἐν θεάτρῳ γε καὶ παντοίοις ἀνθρώποις ᾄδειν ἑστὼς ὀρθὸς ἔτι μᾶλλον αἰσχύνοιτʼ ἄν· καὶ ταῦτά γʼ εἰ καθάπερ οἱ περὶ νίκης χοροὶ ἀγωνιζόμενοι πεφωνασκηκότες ἰσχνοί τε καὶ ἄσιτοι ἀναγκάζοιντο ᾄδειν οἱ τοιοῦτοι, παντάπασίν που ἀηδῶς τε καὶ αἰσχυντηλῶς ᾄδοντες ἀπροθύμως ἂν τοῦτʼ ἐργάζοιντο;

the older he is and the more temperate, the more he will feel ashamed. Is it not so? It is. Surely, then, he will be more than ever ashamed to get up and sing in the theater, before people of all sorts. Moreover, if old men like that were obliged to do as the choristers do, who go lean and fasting when training their voices for a competition, they would assuredly find singing an unpleasant and degrading task, and they would undertake it with no great readiness.