Positive commandment · Mitzvat Aseh #247 of 613
Save the pursued with the life of the pursuer
להציל הנרדף ואפילו בנפש הרודף
The verse · Devarim 25:12
וְקַצֹּתָה אֶת־כַּפָּהּ לֹא תָחוֹס עֵינֶךָ
“then thou shalt cut off her hand, thy eye shall not pity her.”
The Rambam’s words
To save a person who is being pursued even if it is necessary to kill the pursuer, as [Deuteronomy 25:12] states: "And you shall cut off her hand...."
להציל הנרדף ואפילו בנפש הרודף, שנאמר: "וקצותה, את כפה" (דברים כה,יב).
Why · Sefer HaChinuch #600
Save the pursued with the life of the pursuer
“It is from the roots of the commandment [that it is] since G-d, may He be blessed, created His world and wants its settlement; and the settlement of the world is established by the delivery of the weak from the hand of the one stronger than he.”
Who & when
“And [it] is practiced in every place and at all times by males and females.”
Where in the Mishneh Torah
Hilchot Murderer and the Preservation of Life הלכות רוצח ושמירת נפש