Halakhah к Шмот 21:16

The laws of the commandment - for example, that which they said (Mishneh Torah, Laws of Theft 9:6) [that] there is no difference between an adult and a child or between a man and a woman, as "a soul" implies all cases; the law of a father who steals his son or a master who steals his student; and the rest of its details - are [all] elucidated in Chapter Eleven of Sanhedrin. And its prohibition is practiced in every place and at all times. And one who transgresses it and steals a soul is liable for strangulation, and that is if he has already sold that soul. As so came the explanation (Sanhedrin 85b) that the liability does not rest upon him until he sells; since another verse reveals this, as it is written (Exodus 21:16), "And he steals a man and sells him [...], he will surely be killed."

That is that He commanded us to strangle those that transgress certain commandments. And that is His, may He be blessed, saying, "he shall surely be put to death" (Exodus 21:16). And behold, in the negative commandments, we shall [indicate] those which require strangulation. And the regulations of this commandment have already been explained in Tractate Sanhedrin. (See Parashat Kedoshim; Mishneh Torah, The Sanhedrin and the Penalties within their Jurisdiction 14, 15.)

He prohibited - to not steal (kidnap) an Israelite person. And that is His saying in the Ten Commandments, "you shall not steal" (Exodus 20:13). And the language of the Mekhilta (Mekhilta d'Rabbi Yishmael 20:13:3) is, "'You shall not steal,' is the prohibition against stealing a soul." And in the Gemara, Sanhedrin (Sanhedrin 86a) they said, "From where [do we know] the prohibition against stealing souls? Rabbi Yoshiya says, 'From, "you shall not steal."' Rabbi Yochanan says, 'From, "They shall not be sold as slaves" (Leviticus 25:42).' And they do not disagree. One enumerates the prohibition against selling, etc." As they do not execute the punishment upon him until he steals (kidnaps) and sells. But once he transgressed these two negative commandments, he is liable for strangulation - as He, may He be exalted, said, "And one who steals a soul and sells him, etc." (Exodus 21:16). And the regulations of this commandment have already been explained in [Chapter] 1 of Sanhedrin. (See Parashat Yitro; Mishneh Torah, Theft 9.)