Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 297
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 297, with English translation by Maimonides (Rambam).
שלא לעמוד על הדם, שנאמר "לֹא תַעֲמֹד עַל דַּם רֵעֶךָ" (ויקרא יט, טז).
Not to neglect [a person] in mortal danger, as [Leviticus 19:16] states: "Do not stand still in the face of mortal danger."