Kabbalah do Izajasza 57:5

And why all these precautions? — Because otherwise one might emit semen in vain, and Rabbi Yochanan stated: Whosoever emits semen in vain deserves death, since it says (Genesis 38:10) “What he did was unfavorable in the eyes of God and He killed him as well (referring to Onan).” Rabbi Yitzchak and Rabbi Ami said it’s as if he murders, since it says “enflaming yourselves with idols under every green tree, slaying (Shochtei) the children in the valleys under the clefts of the rocks?” (Isaiah 57:5), do not read Shochtei but rather Sochtei (squeeze out).” Rav Asi said: He is like an idol-worshipper; for here it is written, 'Under every green tree' and elsewhere it is written, ‘You shall utterly destroy from all the places where the nations, that you shall possess, worshipped their gods, upon the lofty mountains and upon the hills, and under every green tree.’

In Tractate Kalah (Bride) its says: Rebbi says “’enflaming yourselves with idols’ (Isaiah 57:5), whoever enflames himself to emit semen in vain is considered to be like an animal. Just like an animal does not calculate its actions, has no knowledge of what can cause it death, and does not have a share in the World to Come, so too is he. About him, Solomon said in his wisdom, ‘Who knows the spirit of man whether it goes upward’ (Ecclesiastes 3:21) this alludes to the souls of the Righteous who do not enflame themselves and emit semen in vain. ‘and the spirit of the beast whether it goes downward to the earth?’ (ibid.), this alludes to the souls of the wicked who enflame themselves and emit semen in vain. And whoever enflames himself deserves death, and whoever arouses himself is a renegade, as it says ‘And what he did was evil in the eyes of Hashem" (Genesis 38:7).”

About this sin it says, “Also your clothing is stained with the blood of the innocent and the poor” (Jeremiah 2:34), and also as we said above “slaughterers of children” (Isaiah 57:5) that he literally slaughters his children, and as Rabbi Shimon Bar Yochai says in Vayechi, which we quoted above. Therefore, he does not see the face of the Shechinah, since the Shechinah does not reveal Herself to him as She does to the rest of the Tzadikim, unless he does proper Teshuva, as we will explain later on. Until here is the summary of his words.