You have to believe, by god, that he will be no better in the future after getting this judgment from you and will never stop taking bribes against you if you acquit him.

[οὐ γὰρ δὴ μὰ τὸν Ἡρακλέα βελτίω γενήσεσθαι αὐτὸν προσδοκᾶτε συγγνώμης νυνὶ τυγχάνοντα παρ᾿ ὑμῶν, οὐδὲ τὸ λοιπὸν ἀφέξεσθαι τοῦ λαμβάνειν χρήματα καθ᾿ ὑμῶν, ἐὰν νῦν ἀφῆτε αὐτόν.]

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Dinarchus (c. 361-291 BC) Greek orator and speech writer [Dinarch, Deinarchus, Δείναρχος]
“Against Aristogiton”
    (Source)

Alt. trans.:
  • "Hope not to reform him; for if you pardon him now what assurance have you that he will not against betray your interests in the future?" [tr. Garland (1902)]
  • "For you must assume, by Heracles, that there will be no improvement in him if he is pardoned by you now, and that in future he will not abstain from taking bribes against you if you now acquit him." [tr. Burtt (1962)]