The Talmud discusses the obligation of netilat yadayim before eating bread, tracing it to a rabbinic enactment. It debates the extent of the requirement and whether it applies to all bread or only to terumah, establishing the foundational sugya for this practice.
אָמַר רַב אִידִי בַּר אָבִין, אָמַר רַב יִצְחָק בַּר אַשְׁיָאן: נְטִילַת יָדַיִם לְחוּלִּין, מִפְּנֵי סֶרֶךְ תְּרוּמָה. וְעוֹד מִשּׁוּם מִצְוָה. מַאי מִצְוָה? אֲמַר אַבָּיֵי: מִצְוָה לִשְׁמוֹעַ דִּבְרֵי חֲכָמִים. רָבָא אָמַר: מִצְוָה לִשְׁמוֹעַ דִּבְרֵי רַבִּי אֶלְעָזָר בֶּן עֲרָךְ, דִּכְתִיב: ״וְכֹל אֲשֶׁר יִגַּע בּוֹ הַזָּב וְיָדָיו לֹא שָׁטַף בַּמָּיִם״. אָמַר רַבִּי אֶלְעָזָר בֶּן עֲרָךְ: מִכָּאן סָמְכוּ חֲכָמִים לִנְטִילַת יָדַיִם מִן הַתּוֹרָה.
§ Rav Idi bar Avin says that Rav Yitzḥak bar Ashiyan says: The obligation of washing hands before eating non-sacred food is due to an ancillary decree on account of teruma, the portion of produce designated for the priest, which must be consumed in a state of ritual purity. By rabbinic decree, one’s hands are considered impure with second-degree ritual impurity, as they may have touched impure items. Therefore, they render teruma impure. Consequently, priests who partake of teruma are obligated to wash their hands first. The Sages therefore decreed that all must wash their hands even before eating non-sacred food, so that people not become accustomed to eating without washing their hands, which would in turn lead the priests to partake of teruma without washing their hands. And the obligation is further due to its being a mitzva. The Gemara asks: What mitzva does it involve? Abaye says: It is a mitzva to listen to and obey the statements of the Sages, who instituted this washing of the hands. Rava says: It is a mitzva to listen to the statement of Rabbi Elazar ben Arakh, as it is written with regard to a man who experiences a gonorrhea-like discharge [zav]: “And whomever he that has the issue touches, without having rinsed his hands in water,” he contracts ritual impurity (Leviticus 15:11), and Rabbi Elazar ben Arakh says: From here the Sages based washing of the hands upon a verse from the Torah.