Please advise significant passages where red string is referred to in the 5 books of Moses.
Thank you for your question. Undoubtedly this question troubles many who see the widespread media coverage the red thread has received of late. It is important to know, however, that there is no written mention in the Torah (Five Books of Moses, the Prophets and Writings), Halachah (Jewish Law) or Kabbalah about tying a red string around the wrist. However, it seems to be a custom that has been around for some time, and may be based on Torah or Kabbalistic ideas. If there is any validity to the custom, it would be considered a “segula” or protective type of act.
The original custom seems to have been that, upon giving charity at the Tomb of Rachel, one received a red thread and tied it to the tomb after praying to God. There is basis for mitzvoth (fulfillment of commandments) having a protective nature to them (see Nefesh HaChayim, Rabbi Chayim Volozhin [1853 – 1918]). For example, the Talmud writes, based on a verse in the Torah, that charity protects from natural death, sanctifying the new moon protects from unnatural death, the Succah protects from exile, and so on.
I hope that this sheds some light on the issue for you.