The 243rd prohibition is that we are forbidden from kidnapping any Jewish person.
The source of this prohibition is G‑d's statement in the Ten Commandments,1 "You may not steal."
In the words of the Mechilta: "This verse refers to stealing a person." The Talmud says in tractate Sanhedrin,2 "What is the source for the prohibition of kidnapping? R. Yoshiya says it is the verse, 'You may not steal.' R. Yochanan says it is the verse,3 'They may not be sold as slaves.' In actuality, however, they both agree — one refers to the prohibition of kidnapping and the other refers to the prohibition of selling4 [the kidnapped person." The Talmud mentions these two prohibitions together] because the punishment is given only when the transgressor both kidnaps and sells — and if he does both transgressions, the penalty is strangulation. [The source for the punishment is] G‑d's statement5 (exalted be He), "If one person kidnaps and sells another, and [the victim] is seen in his hand, then [the kidnapper] shall be put to death."
The details of this mitzvah are explained in the 11th chapter of tractate Sanhedrin.6
