Rabbinic Mitzvos #5 Netilas Yadayim
In both a positive mitzvah (#495) and a negative mitzvah (#496), the Torah requires us to follow rabbinic enactments. Seven of these are considered the “Sheva Mitzvos d’Rabbanan,” the “Seven Rabbinic Mitzvos.”
Before eating bread, a person must ritually wash his hands from a utensil. This is true even if he is eating regular bread (as opposed to terumah, which has a degree of sanctity) and even if his hands are clean. The water must be poured using what is called “koach gavra” (i.e., through human effort); sticking one’s hands under running water is insufficient.
The Talmud in Shabbos (14a-b) describes how hands were declared to be ritually impure because they get into everything. Shlomo HaMelech (King Solomon) instituted that we must wash our hands before eating bread. Ultimately, this keeps people from accidentally rendering terumah ritually impure.
Aside from Shabbos 14a-b, this mitzvah is discussed in the tractates of Chulin (106a-107b) and Sotah (4b). It is also the topic of tractate Yadayim in the Mishna. This mitzvah is codified in the Shulchan Aruch in Orach Chaim 158.