Plato, Laws 721c

ἴσχειν πᾶς πᾶσαν· τὸ γὰρ γενέσθαι κλεινὸν καὶ μὴ ἀνώνυμον κεῖσθαι τετελευτηκότα τοῦ τοιούτου ἐστὶν ἐπιθυμία. γένος οὖν ἀνθρώπων ἐστίν τι συμφυὲς τοῦ παντὸς χρόνου, ὃ διὰ τέλους αὐτῷ συνέπεται καὶ συνέψεται, τούτῳ τῷ τρόπῳ ἀθάνατον ὄν, τῷ παῖδας παίδων καταλειπόμενον, ταὐτὸν καὶ ἓν ὂν ἀεί, γενέσει τῆς ἀθανασίας μετειληφέναι· τούτου δὴ ἀποστερεῖν ἑκόντα ἑαυτὸν οὐδέποτε ὅσιον, ἐκ προνοίας δὲ ἀποστερεῖ ὃς ἂν παίδων καὶ γυναικὸς ἀμελῇ. πειθόμενος

The desire to win glory, instead of lying in a nameless grave, aims at a like object. Thus mankind is by nature coeval with the whole of time, in that it accompanies it continually both now and in the future; and the means by which it is immortal is this:—by leaving behind it children’s children and continuing ever one and the same, it thus by reproduction shares in immortality. That a man should deprive himself thereof voluntarily is never an act of holiness; and he who denies himself wife and children is guilty of such intentional deprivation.