In Parshat Lech L’cha, the King of Sodom offers Avraham all the loot retrieved from the war of the 4 kings and the 5 kings (Genesis 14:21).
Avraham swears in the name of Hashem that he will not take one iota, namely “From a string to a shoelace,” from the king so that he will not be able to say “I made Avraham rich!” (Genesis 14:23)
The Talmud (Sotah 17a) quotes the following Midrash: As a reward for Avraham’s refusing the king’s offer with the words, “From a string to a shoelace” his children were rewarded with two mitzvot: the Tekhelet string, and the Tefillin strap!
