Y'all shall therefore keep My statutes, and My ordinances, which if a person does, s/he shall live by them: I am Ad-nai.
A Baraita: There was an incident involving ben Dama, son of Rabbi Yishmael’s sister, in which a snake bit him. And following the attack, Ya’akov of the village of Sekhanya, who was a heretic came to treat him, but Rabbi Yishmael did not let him do so. And ben Dama said to him: Rabbi Yishmael, my brother, let him treat me, and I will be healed by him. And I will cite a verse from the Torah to prove that accepting medical treatment from a heretic is permitted in this situation. But ben Dama did not manage to complete the statement before his soul departed from his body and he died. Rabbi Yishmael recited with regard to him: Fortunate are you, ben Dama, as your body is pure and your soul departed in purity, and you did not transgress the statement of your colleagues, who would state the verse: “And who breaks through a fence, a snake shall bite him” (Ecclesiastes 10:8), i.e., one is punished for ignoring an ordinance of the Sages. This incident indicates that it is not permitted for one to accept medical treatment from a heretic even if it is clear that without it he will live only a short while. The Gemara explains: Heresy is different, as it is enticing. In other words, it is prohibited to accept medical treatment from a heretic, as one might come to be drawn after his heresy. By contrast, receiving medical attention from a gentile is permitted if it is certain that one will die if he is not treated. The Master said above: You did not transgress the statement of your colleagues, who would state the verse: “And who breaks through a fence, a snake shall bite him.” The Gemara asks: But ben Dama was also bitten by a snake, even before this declaration of Rabbi Yishmael, so how can he be considered fortunate? The Gemara explains: The snake mentioned in the curse of the Sages is different, as it has no remedy whatsoever. Although ben Dama was bitten by a snake, he could have been healed. The Gemara asks: And what would ben Dama have said? What verse did he intend to cite as proof that it was permitted for him to be healed by a heretic? The verse: “You shall therefore keep My statutes, and My ordinances, which if a man do, he shall live by them” (Leviticus 18:5). This teaches that one should live by God’s mitzvot, and not that he should die by them. This verse serves as a source for the halakha that one may violate a prohibition in order to save a life.
(ו) הָאִשָּׁה שֶׁהִיא מַקְשָׁה לֵילֵד, מְחַתְּכִין אֶת הַוָּלָד בְּמֵעֶיהָ וּמוֹצִיאִין אוֹתוֹ אֵבָרִים אֵבָרִים, מִפְּנֵי שֶׁחַיֶּיהָ קוֹדְמִין לְחַיָּיו. יָצָא רֻבּוֹ, אֵין נוֹגְעִין בּוֹ, שֶׁאֵין דּוֹחִין נֶפֶשׁ מִפְּנֵי נָפֶשׁ:
(6) If a woman is having trouble giving birth, they cut up the child in her womb and brings it forth limb by limb, because her life comes before the life of [the child]. But if the greater part has come out, one may not touch it, for one may not set aside one person's life for that of another.
The reason why a person may not push aside someone else’s life (to save his own life) is that if A kills B, there will be two negative consequences: B’s death and a transgression of a sin. However, if A remains passive, there will be one negative consequence: A’s death, but he will not transgress. The Torah only permitted us to violate mitzvot based on the dispensation "and you shall live by them" because a Jewish life is [more] precious to God [than mitzvot]. However, here, [the dispensation does not apply] since one Jewish life will be any way lost in the end, why should it be permitted to transgress? Who knows that your [A] life is more dear to God than your friend's [B] life? Therefore the Place said: it is not possible to push aside.
What did you see to say that your blood is redder? - How can you know that your blood is more precious and pleasant to your Creator than the blood of your fellow? Therefore, one cannot say here "'and live by them' - and not die by them" since Scripture only permitted [the dispensation] due to the Holy One of Blessing's love of the souls of Israel, and here since the destruction of the life of the fellow the word of the King does not give permission for pushing aside [the prohibition of] killing.
(כג) סיעה של בני אדם שאמרו להם נכרים תנו לנו א' מכם ונהרגהו ואם לאו הרי אנו הורגין את כולן יהרגו כולן ואל ימסרו להם נפש אחת מישראל אבל אם ייחדוהו להם כגון שיחדו לשבע בן בכרי יתנוהו להם ואל יהרגו א"ר יהודה בד"א בזמן שהוא [מבפנים והן] מבחוץ אבל בזמן שהוא מבפנים והם מבפנים הואיל והוא נהרג והן נהרגין יתנוהו להן ואל יהרגו כולן וכן הוא אומר (שמואל ב כ) ותבא האשה אל כל העם בחכמתה וגו' אמרה להם הואיל והוא נהרג ואתם נהרגין תנוהו להם ואל תהרגו כולכם ר"ש אומר כך אמרה [להם] כל המורד במלכות [בית דוד] חייב מיתה.
(23) A group of [Jews] to whom gentiles say, “Give us one of you and we shall kill him, and if not, behold, we will kill all of them”; they should let themselves be killed and not deliver them one soul from Israel. But if they designated [the person] to them – for example, Sheva ben Bichri – they should give him to them and not let themselves be killed. Rabbi Yehuda said, “When do these words apply? In a case when he is [inside and they are] outside [a fortified city]; but in a case when he is inside and they are inside, since he will be killed and the [other Jews] will be killed, they should give him to them and not let themselves all be killed. And so did it state (II Samuel 20:22), ‘And the woman come to all of the people in her wisdom, etc.’ – she said to them, ‘Since he will be killed and you will be killed, give him to them and do not kill all of you.’” Rabbi Shimon says, “So did she say [to them], ‘Anyone who rebels against the monarchy [of the House of David] is liable to [receive] the death penalty.’”
תני סיעות בני אדם שהיו מהלכין בדרך פגעו להן גוים ואמרו תנו לנו אחד מכם ונהרוג אותו ואם לאו הרי אנו הורגים את כולכם אפי' כולן נהרגים לא ימסרו נפש אחת מישראל ייחדו להן אחד כגון שבע בן בכרי ימסרו אותו ואל ייהרגו א"ר שמעון בן לקיש והוא שיהא חייב מיתה כשבע בן בכרי ורבי יוחנן אמר אע"פ שאינו חייב מיתה כשבע בן בכרי עולא בר קושב תבעתיה מלכותא ערק ואזיל ליה ללוד גבי ריב"ל אתון ואקפון מדינתא אמרו להן אין לית אתון יהבון ליה לן אנן מחרבין מדינתא סלק גביה ריב"ל ופייסיה ויהביה לון והוה אליהו זכור לטוב יליף מתגלי עלוי ולא אתגלי וצם כמה צומין ואיתגלי עלוי אמר ליה ולמסורות אני נגלה א"ל ולא משנה עשיתי א"ל וזו משנת החסידים
It is taught: caravans of [Jewish] people that were on a journey and met idol worshipers who said "Give us one of your group so that we may kill him otherwise we will kill all of you!" Even if the entire group of Jews will be killed it is forbidden to give up a single Jew to be killed. But if they demand a specific Jew by name, such as Sheva Ben Bichri they give that person up and are not killed. Says Rabbi Shimeon Ben Lakish: this only applies if the person specified had a death penalty upon him, like Sheva Ben Bichri. And Rabbi Yochanan [disagrees and] says even if he does not have the death penalty upon him [they give the specified individual up].
Ullah bar Koshev was wanted by the [Roman] Kingdom. He fled and went to Lod, to Rabbi Yehoshua Ben Levi's. They came and surrounded the city, and they said: if you don't give him to us, we will destroy de city. Rabbi Yehoshua Ben Levi went to him [Ullah] and appeased him, and gave him [to the Roman authorities]. And Eliahu [Hanavi], may he be remembered for good, would teach him [RYBL] and reveal himself to him, and he did not reveal himself [anymore]. He fasted several fasts, and he [Eliahu] revealed himself. He said: "And I reveal myself to informers?!" He [RYBL] responded: "And didn't I do [according to] a rabbinic teaching?" And [Eliahu] answered: "And is this a teaching for the pious?!"