The Ruling on Swearing by a Religion Other Than Islam

Question:
There is a person who claims about himself that he will become a Jew if he does not do such and such, or such and such. He says: "I am a Jew who does not do such and such."

Answer:
This is not permissible. It came in a hadith from the Prophet (peace and blessings be upon him) who said: And in the other narration: So it is not permissible for a person to say: "I am a Jew who does not talk to so-and-so," or "I am a Christian who does not talk to so-and-so," or "I am a polytheist who does not talk to so-and-so." This speech is not permissible. However, he does not become a disbeliever by this; he becomes a sinner and wrongs himself, because he did not intend disbelief, but rather intended to be strict with himself and to emphasize that he would not talk to so-and-so. He did not intend that he is a Jew, so he does not become a disbeliever by this, but he becomes a sinner.
As for if he says: "I am a Jew or a Christian"—meaning he intends the belief and the transition from Islam to Judaism, and that he chooses Judaism—he becomes a disbeliever. If he says "I am a Jew," meaning that I leave my religion and choose Judaism, or Christianity, or Zoroastrianism, or Communism, or the like, and if he says this while desiring these religions, he becomes a disbeliever in Allah—may we seek refuge in Allah—an apostate who is asked to repent. If he repents, well and good; otherwise, he is killed.