I somehow come across a Question in Quora that claim did Muhammad(sw)copied from Thalmud as Sura 5:32 and Misnah Sanhedrin 4:5 is too similar,I dont have much knowledge about it so after googling I told if Misnah is Oral torah than God just confirmed it in Quran but she show me this "English Explanation of Mishnah Sanhedrin 4:5:1" https://www.sefaria.org/English_Explanation_of_Mishnah_Sanhedrin.4.5.1?lang=bi, What does it mean?Was this jewish law created by jewish rabbi and not oral torah?She also mocked that Quran challenged no one would be able to produce a work like it but people already produced something like that way before Quran and Quran copied it. Actually what is this misnah sanhedrin and how to reconcile this with Quran?
Quran 5:32 says
Because of that We ordained for the Children of Israel: that whoever kills a person—unless it is for murder or corruption on earth—it is as if he killed the whole of mankind; and whoever saves it, it is as if he saved the whole of mankind. Our messengers came to them with clarifications, but even after that, many of them continue to commit excesses in the land.
What you cited is a comment on the comment on Genesis 4:15
But the Lord said to him, “Not so e ; anyone who kills Cain will suffer vengeance seven times over.” Then the Lord put a mark on Cain so that no one who found him would kill him.
The Mishnah Torah is oral (scholarly) tradition and comment on the Torah. It has been written down by Jews later than Jesus but before Muhammad according to older oral traditions and common fiqh. Orthodox and Conservative Jews consider it part of the Torah. The Jews call it the "Oral Torah", not claiming that all written in there is part of the Torah but containing old traditions said to root in the teachings of Mose. It says
The court tells the witnesses: Therefore, Adam the first man was created alone, to teach you that with regard to anyone who destroys one soul from the Jewish people, i.e., kills one Jew, the verse ascribes him blame as if he destroyed an entire world, as Adam was one person, from whom the population of an entire world came forth.
Indeed, we have here one of the few examples where the Quran cites something that is only contained in the Oral Torah as part of the Torah, and to my knowledge the only one where it is confirming it to be ordained to the Children of Israel.
Note that the Quran is not the first but the last revelation, essentially confirming what has been revealed before. So do not be astonished to find many many things that have been said before.