Handwashing in Judaism (English Wikipedia)

Tosafot, Chullin 106a; see also Netziv, Leviticus 15:11 which appears to link handwashing to the possibility of a dirty hand transferring ritually impure bodily fluids.

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Berlin, Adele, ed. (2011). "Cleanliness". The Oxford Dictionary of the Jewish Religion. New York: Oxford University Press. ISBN 9780199730049. The Shulkhan Arukh (Orach Chayim 4:18, 158-165) lists occasions when hands should be washed; upon arising each morning, after urination and defecation, after taking off one's shoes, or touching any part of the body customarily covered, after visiting a cemetery, after undressing, before and after meals, after marital relations, and after coming into contact with lice.

Hadad Brothers. "Mayim Achronim Set". Hadad Brothers. Archived from the original on 2 April 2015. Retrieved 16 August 2010.

Maimonides, Mishneh Torah, Hil. Berakhot 6:2), following a teaching that says: "All of the commandments, entirely, one is to [first] make the blessing [over them before performing the act], and then he proceeds into their actual performance" (Sukkah 39a; Pesaḥim 7b). The author of Sefer Ha-Eshkol also required reciting the blessing before pouring water over one's hands, saying that any uncleanness which would not hinder one's prayer does not hinder the blessing said over hand washing (q.v. Sefer Ha-Eshkol, Berlin 1910, page 50 [Hebrew]).
Compare responsum of Hai Gaon quoted in Sefer Shaarei Teshuvah - 353 Geonic Responsa (Leipzig 1858), responsum 196 (Hebrew).

1 Kings 7:38
Babylonian Talmud, Hullin 106a. Based on Leviticus 15:11, Rava explained the verse as follows: "What is the meaning of that which is written, 'while he has not rinsed his hands in water?' Behold! Had he rinsed [his hands], would he be ritually clean?! Behold! He [still] requires an immersion [in a ritual bath]!! Rather, this is its meaning. After [he had immersed himself], so long as he has not yet rinsed [his hands], he is [still] unclean!"

"Berakhot 53b:32". www.sefaria.org.
"Yoma 83b:16". www.sefaria.org.
Mishnah, Yoma 3:2; the word "urinating" is written with a euphemism, lit. "anyone who pours water." See: Mishnah Yoma, chapter 3
"Shabbat 13b:9". www.sefaria.org.
Pesachim 115b and comments of Rashi and Rashbam; Rashi, Yoma 30a; Hebrew-English Edition of Babylonian Talmud - Shabbath, (ed. Rabbi Dr. H. Freedman), The Soncino Press London 1987, s.v. Shabbath 14a, note 7
Shabbat 14a
"Shabbat 14b:6". www.sefaria.org.

Chullin 105b; see also Berachot 53b where the purpose appears to be to sanctify one's hands before reciting Birkat Hamazon. The Rishonim reconcile these sources in various ways.
Eruvin 21b, Shabbat 14b-15a
Shabbat 11a^{[permanent dead link‍]} and Ketubbot 50b^{[permanent dead link‍]}: והלל ושמאי גזרו על טהרת ידיים. רבי יוסי בי רבי בון בשם רבי לוי: כך היתה הלכה בידם ושכחוה ועמדו השניים והסכימו על דעת הראשונים.‎
Babylonian Talmud, Hullin 106a. Based on Leviticus 15:11, Rava explained the verse as follows: "What is the meaning of that which is written, 'while he has not rinsed his hands in water?' Behold! Had he rinsed [his hands], would he be ritually clean?! Behold! He [still] requires an immersion [in a ritual bath]!! Rather, this is its meaning. After [he had immersed himself], so long as he has not yet rinsed [his hands], he is [still] unclean!"
Babylonian Talmud, Chullin 106a

Hadad Brothers. "Mayim Achronim Set". Hadad Brothers. Archived from the original on 2 April 2015. Retrieved 16 August 2010.

Eisenstein, Judah D. (1970). A Digest of Jewish Laws and Customs - in Alphabetical Order (Ozar Dinim u-Minhagim) (in Hebrew). Tel-Aviv: Ḥ. mo. l. p. 267 (s.v. נטילת ידים). OCLC 54817857. (reprinted from 1922 and 1938 editions of the Hebrew Publishing Co., New York)