Plato, Laws 847a

ἐκείνων διὰ τὸ τὴν πρόσοδον ἐκεῖθεν αὑτῷ πλείω γίγνεσθαι τῆς αὑτοῦ τέχνης, ἀλλʼ εἷς μίαν ἕκαστος τέχνην ἐν πόλει κεκτημένος ἀπὸ ταύτης ἅμα καὶ τὸ ζῆν κτάσθω. τοῦτον δὴ τὸν νόμον ἀστυνόμοι διαπονούμενοι σῳζόντων, καὶ τὸν μὲν ἐπιχώριον, ἐὰν εἴς τινα τέχνην ἀποκλίνῃ μᾶλλον ἢ τὴν τῆς ἀρετῆς ἐπιμέλειαν, κολαζόντων ὀνείδεσί τε καὶ ἀτιμίαις, μέχριπερ ἂν κατευθύνωσιν εἰς τὸν αὑτοῦ δρόμον, ξένων δὲ ἄν τις ἐπιτηδεύῃ δύο τέχνας, δεσμοῖσί τε καὶ χρημάτων

from that source than from his own craft; but each several craftsman in the State shall have one single craft, and gain from it his living. This law the city-stewards shall labor to guard, and they shall punish the resident citizen, if he turn aside to any craft rather than to the pursuit of virtue, with reproofs and degradation, until they restore him to his own proper course; and if a foreigner pursue two crafts, they shall punish him by imprisonment, money-fines,