Enchiridion · §14

ἐὰν θέλῃς τὰ τέκνα σου καὶ τὴν γυναῖκα καὶ τοὺς φίλους σου πάντοτε ζῆν, ἠλίθιος εἶ· τὰ γὰρ μὴ ἐπὶ σοὶ ὄντα θέλεις ἐπὶ σοί εἶναι, καὶ τὰ ἀλλότρια σά.κύριος ἑκάστου ἐστὶν ὁ τῶν ὑπ᾽ αὐτοῦ θελομένων ἢ μὴ θελομένων ἔχων τὴν ἐξουσίαν τοῦ περιποιεῖν ἢ ἀφαιρεῖσθαι. ὅστις οὖν ἐλεύθερος εἶναι βούλεται, μήτε θελέτω τι μήτε φευγέτω τι τῶν ἐπ᾽ ἄλλοις· εἰ δὲ μή, δουλεύειν ἀνάγκη.

ean thelēs ta tekna sou kai tēn gunaika kai tous philous sou pantote zēn, ēlithios ei; ta gar mē epi soi onta theleis epi soi einai, kai ta allotria sa. hostis oun eleutheros einai bouletai, mēte theletō ti mēte pheugetō ti tōn ep' allois; ei de mē, douleuein anankē.

If you wish your children, your wife, and your friends to live forever, you are a fool — for you are wishing that things outside your control were within it, and that what belongs to others were yours. In the same way, if you want your servant never to make a mistake, you are stupid. Whoever wishes to be free must neither desire nor avoid anything that depends on others. Otherwise, slavery is inevitable.

— Enchiridion 14

Source: Greek (Schenkl/Oldfather critical edition tradition) + Long 1877 English translation