Kabbalah su Salmi 5:5

Come and behold: all of man's sins and corruption can be atoned for by repentance. But by the sin of spilling his seed on the earth, man corrupts himself and the earth as well. And of such a person, it is written: "The stain of your iniquity is before Me," (Yirmeyah 2:22) and "For You are not an El that has pleasure in wickedness, nor shall evil sojourn with You" (Tehilim 5:5). (For the sin of spilling seed, He does not accept his repentance) except after great penitence. It is also written that "Er, Judah's firstborn, was wicked in the sight of Hashem; and Hashem slew him" (Gen. 38:7), as was already explained elsewhere.

Rav stated: 'A man who willfully causes erection should be placed under the ban'. But why did he not say, 'This is forbidden'? Because the man merely incites his evil inclination against himself. Rav Ami, however, stated: He is called a renegade, because such is the art of the evil inclination: today it incites man to do one wrong thing, and tomorrow it incites him to worship idols and he proceeds to worship them. There are others who say that Rav Ami stated, He who excites himself by lustful thoughts will not be allowed to enter the division of the Holy One, blessed be He. For here it is written, “was evil in the eyes of Hashem" (Genesis 38:7), and elsewhere it is written, “For You are not El who has pleasure in wickedness; nor shall evil dwell with you” (Tehilim 5:5). Rav Elazar stated: Who are referred to in the Scriptural text, “Your hands are full of blood” (Isaiah 1:15)? Those that commit masturbation with their hands. It was taught at the school of Rabbi Yishmael, ‘Thou shalt not commit adultery’ implies, Thou shalt not practice masturbation either with hand or with foot. Our Rabbis taught: 'proselytes and those that play with children delay the advent of the Messiah', meaning: Those that marry minors who are not capable of bearing children, for Rav Yosi stated: The Son of David will not come until all the souls in Guf (Lit. 'Body' the region inhabited by the souls of the unborn) will have been disposed of, since it says, “For the spirit that humbles itself is from Me, and the souls which I have made” (Isaiah 57:16).

In the Zohar they were very stringent about this sin, and this is what it says: (Zohar with Sulam commentary, Beresheet B) 393. Of the verse, "For You are not El who has pleasure in wickedness; nor shall evil dwell with you" (Tehilim 5:5), Rabbi Yehuda said: This verse has been discussed and explained, yet come and behold: he who cleaves to and is led by the Evil Inclination is defiled and will be led further into defilement, as we have learned. 394. "The wickedness of man was great," because men committed all sorts of sins and their guilt was complete when they spilled blood in vain upon the ground. This refers to those who pollute their ways upon the earth, THAT IS, THEY SPILL THEIR SPERM IN VAIN. Thus, it is written: "Only evil (Heb. ra) all day." In another place it is written: "And Er, the son of Judah, was evil (Heb. ra) in the eyes of Hashem" (Beresheet 38:7), BECAUSE HE SPILLED HIS SEED UPON THE EARTH. THIS INDICATES THAT THE WORD RA REFERS TO THE WASTE OF SEED.