Leviticus 15:3

And this shall be his uncleanness in his issue: whether his flesh run with his issue, or his flesh be stopped from his issue, it is his uncleanness.

Onkelos Targum
ודא תהי סאובתיה בדוביה ריר בסריה ית דוביה או חתים בסריה מדוביה סאובתיה היא

Septuagint
καὶ οὗτος ὁ νόμος τῆς ἀκαθαρσίας αὐτοῦ ῥέων γόνον ἐκ σώματος αὐτοῦ ἐκ τῆς ῥύσεως ἧς συνέστηκεν τὸ σῶμα αὐτοῦ διὰ τῆς ῥύσεως αὕτη ἡ ἀκαθαρσία αὐτοῦ ἐν αὐτῷ πᾶσαι αἱ ἡμέραι ῥύσεως σώματος αὐτοῦ ᾗ συνέστηκεν τὸ σῶμα αὐτοῦ διὰ τῆς ῥύσεως ἀκαθαρσία αὐτοῦ ἐστιν

Origen, Fragments on 1 Corinthians 31 (On 1 Cor. 6:18)
φεύγετε τὴν πορνείαν· πᾶν ἁμάρτημα ὃ ἐὰν ποιήσῃ ἄνθρωπος ἐκτὸς τοῦ σώματός ἐστιν, ὁ δὲ πορνεύων εἰς τὸ ἴδιον σῶμα ἁμαρτάνει.  Ζητήσει τις, εἰ πᾶν ἁμάρτημα ἐκτὸς τοῦ σώματός ἐστιν. ἐρεῖ γάρ τιςἉμάρτημά ἐστι τὸ μεθύειν· ἁμάρτημά ἐστι τὸ ἑαυτὸν ἐξάγειν ἐκ τοῦ βίου δι’ ἀγχόνης, διὰ κρημνοῦ· ἆρ’ οὖν ἐκτὸς τοῦ σώματός ἐστι καὶ τοῦτο τὸ ἁμάρτημα; ἀλλ’ εὐγνωμόνως δεῖ ἀκοῦσαι πῶς εἴρηται τοῦτο· ἀφορμὴν δὲ ληψόμεθα τοῦ νοῆσαι τὰ κατὰ τὸν τόπον ἐκ τοῦ Λευϊτικοῦ· ἐκεῖ γὰρ λέγεται ὅτι ἐκ τῆϲ ῥύϲεωϲ ϲυνέϲτηκεν τὸ ϲῶμα αὐτοῦ. ἐπεὶ οὖν ἡ σύστασις τοῦ σώματος ἀπὸ σπερμάτων ἐστί, διὰ τοῦτο ὁ ἁμαρτάνων κατὰ τὴν πρόρρυσιν τῶν σπερμάτων εἰς τὸ σῶμα τὸ ἑαυτοῦ ἁμαρτάνει· καὶ ἔστιν ἡ ἁμαρτία αὕτη ἀπὸ τούτων γινομένη, ἀφ’ ὧν καὶ ἡ ἀρχὴ τῆς συστάσεως τοῦ σώματος.

"Flee from sexual immorality. Every other sin a person commits is outside the body, but the sexually immoral person sins against his own body" (1 Cor. 6:18). Some ask, if indeed every sin is outside of the body. For he enquires if to be drunken is a sin, if taking your own life by hanging is a sin. So outside the body is also a sin, but you need to hear wisely how he asks this. And w e can start by receiving a thought from a passage in Leviticus: for there it is said that “from the flow his body is compacted” (Lev. 15:3). Since the compacting of the body is from the sperm, therefore one who sins by the flow of sperm, sins in his own body. And his sins are from this, that it is the origin of the compacting of the body.