Gemara

Even though the witnesses retracted, we carry out the sentence, even if though they gave a reason (why they lied).

Kesuvos 60b (Beraisa): Even if meager food was stipulated (for a nursing woman), she must still eat well. She may not eat things bad for the milk.

(Rav Sheshes): She pays for the extra food.

Nedarim 80b (Beraisa): If water from a spring of the city is needed to sustain the life of outsiders, the laundry of the city residents has precedence;

R. Yosi says, the laundry of city residents has precedence over the life of others.

R. Yosi holds that refraining from laundering causes pain.

Avodah Zarah 28b: Shmuel taught that one may apply a potion to an eye about to leave the socket on Shabbos, because nerves connect the eye to the heart.

Rishonim

Rambam (Hilchos Rotze'ach 1:14): Anyone who could save (someone being pursued), but did not, transgressed "Lo Sa'amod Al Dam Re'echa."

Kesef Mishneh: Hagahos Maimoniyos says that the Yerushalmi (Terumos 8:4) concludes that one must enter Safek danger to save another. It seems that this is because the other is in definite danger.

Bach (CM 426:2): The Beraisa connotes that even if it is not clear that he will be able to save, he must enter Safek danger to try. However, the Rambam wrote 'he could save', which connotes that that he surely could save. This is why the Tur says 'and the Rambam says...', for he rules unlike this.

Rambam (Hilchos Rotze'ach 7:8): A Shogeg murderer who went to exile never leaves before the Kohen Gadol dies, even to save a life with his testimony, or to save from an army, river or fire or house that collapsed. Even if all Yisrael need him, like Yo'av, he does not leaves until the Kohen Gadol dies. If he leaves, he permits himself to be killed, like we explained.

Or Some'ach: The Rambam added the reason he may not leave, for Piku'ach Nefesh overrides (almost) all Mitzvos, especially Piku'ach Nefesh for all of Yisrael. Esther (going to Achashverosh) proves this. However, we should not go against nature - "the Go'el ha'Dam's heart will be hot to kill him; he is not liable to die." Therefore, the murderer should not put himself in Safek danger to save another from Vadai danger, unlike the Kesef Mishneh cited from the Yerushalmi. Really, there is no proof from the Yerushalmi.

Rambam (Hilchos Ishus 21:11): If we apportioned proper food for her (a nursing woman) and she desires more or other foods due to the hunger in her stomach, she eats from her money as much as she wants. Her husband cannot protest and say that excess or bad foods will kill the child, for her pain has precedence.

Rebuttal (Ra'avad): The Gemara said only that if she needs more food for the need of the baby, her husband pays for it.

Magid Mishneh: The Beraisa forbids eating things bad for milk! We must say that this is when she not in pain. If she is in pain, her pain has precedence.

Question (Kesef Mishneh): Her life has precedence over the Bas Yisrael's life, but her pain does not! Also, why didn't the Rambam teach about when she is not in pain? Rather, the Beraisa permits eating extra, even though this is bad for the milk. We cannot say that the Beraisa forbids foods bad for milk. We must say that it teaches that he cannot stop her from eating such foods.

Gra (EH 80:21): This requires investigation.

Radvaz (3:627 (1052)): Some say that if a lord told Reuven 'let me cut a non-vital limb from you, or else I will kill Shimon', that Reuven must forfeit the limb. One may cure an eye on Shabbos due to mortal danger. Shabbos is severe. Saving a (non-vital) limb does not override it, yet we override it for Piku'ach Nefesh. Shabbos overrides a limb, all the more so Piku'ach Nefesh overrides a limb! I say that this is mere Midas Chasidus. The Kal va'Chomer is invalid. Danger to a limb does not override Shabbos because it is an Ones from Shamayim. This is no source to obligate putting Ones upon oneself for the sake of another. Also, perhaps one will bleed to death from cutting off a limb. I saw a man die from mere scratches on the ear to draw blood. Who says that another's blood is redder than yours?! Also, the limbs are obligated to observe Shabbos - "one will live in them (Mitzvos)", he will not die in them. If not for this verse, one might have thought that we do not override even for mortal sickness. One need not sacrifice himself to save another. One must use his money to save others, but he need not endanger his limbs. Further, we do not punish due to a Kal va'Chomer. Losing a limb is the ultimate punishment. It is harsher than lashes. We do not literally fulfill "an eye for an eye... a burn for a burn", lest he die, and an eye and a life were in place of an eye. There is more mortal danger from cutting off a limb than from a burn! Also, "its ways are pleasant" - logic does not tolerate that one must forfeit his eye, hand or leg to save another. It is Midas Chasidus; happy is one who can fulfill this. If it is mortal danger, he is a crazy Chasid. The Safek of his life overrides the certain death of his friend.

Or Some'ach (ibid.): I saw in the name of the Radvaz that one must forfeit a limb in order to save another. This is wrong. A support is Sanhedrin 44b, which says that even if witnesses retract and give a reason (why they lied), we carry out the sentence. We do not say that they should cut off their hands to exempt the Nidon (the one convicted), for we cannot fulfill "the hands of the witnesses will be first", even though they unjustly caused his execution.

Rebuttal (Divrei Yatziv CM 79:35): If the witnesses do not want to cut off their hands, Beis Din cannot force them, because one cannot retract his testimony. We believe their initial words, that the Nidon deserves to die.

Yachel Yisrael (68 DH v'Hinei): Rashi explains that the Nidon was sentenced to be stoned. It suffices for the witnesses not to stone him!

Tal Torah (45b DH Nikta'ah): The Gemara connotes that as long as the witnesses still have hands, we can kill the Nidon even if the witnesses refuse. However, the Rambam, Kesef Mishneh and Tumim (33:4, b'Sof) hold that the witnesses must begin (except for a murderer).

Gilyonei ha'Shas (Sanhedrin 73a DH Minayin): Maharamam says that if one can cause that another will lose only a limb instead of his life, he must do so. He was unsure if it is better to tell the judge to deprive him of money than a limb. If money is more severe, since one must use his money to save another, all the more so he must forfeit a limb to save another. Perhaps Maharamam was unsure if losing all one's money is worse than losing a limb.

Poskim

Shulchan Aruch (CM 426:1): If Reuven sees Shimon drowning, or bandits are pursuing him, or a vicious animal is coming upon him, and Reuven himself could have saved him or hired others to save him, but he did not, he transgressed "Lo Sa'amod Al Dam Re'echa."

SMA (2): Hagahos Maimoniyos says that one must enter Safek danger to save another, for the other is in definite danger. Perhaps the Shulchan Aruch and Rema omitted this because the Rif, Rambam and Rosh did not bring it.

Shulchan Aruch (EH 80:12): If a nursing woman desires foods that are not good for the baby, some say that her husband cannot stop her, for her pain overrides danger to the baby. Some say that he can stop her.

Chelkas Mechokek (22): If there is Safek danger to the child and her concern is only pain, surely her pain does not override! If there is also danger for her, who would say that he can stop her?!

Beis Shmuel (15): The Rambam holds that he cannot stop her. We find that R. Yosi holds that one's pain (inability to wash clothes) overrides others' lives. However, why does the Rambam rule like R. Yosi against Chachamim?!

Hagahos ha'Rim (in Rosh Pinah Shulchan Aruch): The Rambam discusses a pregnant woman. The fetus is not yet considered a Nefesh, therefore her pain takes precedence. Perhaps we discuss when she is not visibly pregnant; her increased or changed appetite arouses suspicion that she is pregnant.

Shai l'Mora (ibid.): Also the She'altos (Parshas Re'eh) rules like R. Yosi. Why did the Tur, Shulchan Aruch and Rambam omit the law (of laundering)?