Plato, Letters 311c

ὅτι οὐκ, ἐπειδὰν ἡμεῖς τελευτήσωμεν, καὶ οἱ λόγοι οἱ περὶ ἡμῶν αὐτῶν σεσιγήσονται· ὥστʼ ἐπιμελητέον αὐτῶν ἐστιν. ἀνάγκη γάρ, ὡς ἔοικε, μέλειν ἡμῖν καὶ τοῦ ἔπειτα χρόνου, ἐπειδὴ καὶ τυγχάνουσιν κατά τινα φύσιν οἱ μὲν ἀνδραποδωδέστατοι οὐδὲν φροντίζοντες αὐτοῦ, οἱ δʼ ἐπιεικέστατοι πᾶν ποιοῦντες ὅπως ἂν εἰς τὸν ἔπειτα χρόνον εὖ ἀκούσωσιν. ὃ δὴ καὶ ἐγὼ τεκμήριον ποιοῦμαι ὅτι ἔστιν τις αἴσθησις τοῖς τεθνεῶσιν τῶν ἐνθάδε· αἱ γὰρ βέλτισται

men’s talk about us will not likewise be silenced; so that we must be careful about it. We must necessarily, it seems, have a care also for the future, seeing that, by some law of nature, the most slavish men pay no regard to it, whereas the most upright do all they can to ensure that they shall be well spoken of in the future. Now I count this as a proof that the dead have some perception of things here on earth; for the best souls divine that this is so,