Plato, Laws 873a

τὸ μιανθὲν πρὶν φόνον φόνῳ ὁμοίῳ ὅμοιον ἡ δράσασα ψυχὴ τείσῃ καὶ πάσης τῆς συγγενείας τὸν θυμὸν ἀφιλασαμένη κοιμίσῃ. ταῦτα δὴ παρὰ θεῶν μέν τινα φοβούμενον τὰς τιμωρίας εἴργεσθαι χρὴ τὰς τοιαύτας· εἰ δέ τινας οὕτως ἀθλία συμφορὰ καταλάβοι, ὥστε πατρὸς ἢ μητρὸς ἢ ἀδελφῶν ἢ τέκνων ἐκ προνοίας ἑκουσίως ψυχὴν τολμῆσαι ἀποστερεῖν σώματος, ὁ παρὰ τοῦ θνητοῦ νομοθέτου νόμος ὧδε περὶ τῶν

before the soul which committed the act pays back murder for murder, like for like, and thus by propitiation lays to rest the wrath of all the kindred. Wherefore, in dread of such vengeances from Heaven a man should refrain himself; if, however, any should be overtaken by a disaster so lamentable that they have the audacity deliberately and of free will to reave soul from body for father, mother, brethren or children, in such cases the ordinance of the law of the mortal lawgiver stands thus:—