The commandment of tzitzit is one of the 613 mitzvahs in the Torah. According to this mitzvah, he who has a garment with four corners (knafot) must have four groups of fringes attached to the garment, one to each of the corners.
The Origin of the Mitzvah
The commandment to wear tzitzit appears in the book of Numbers, 15:38-39:
“Speak unto the children of Israel, and tell them that they make them fringes (tzitziot) in the borders of their garments throughout their generations, and that they put upon the fringe (tzitzit) of the borders a chord of light blue. And it shall be unto you for a fringe, that ye may look upon it, and remember all the commandments of the Lord, and do them; and that ye seek not after your own heart and your own eyes, after which ye use to go a whoring.”
How is the Tzitzit tied, and What are the 7-8-11-13 Knots?
The obligation to make a knot using four threads (ptilim, the word tzitzit signifying a group of dangling strings, as in a braid, which can be seen as a tzitzit on one’s head), that are interwoven into the four corners of a garment possessing four angular corners or more appears in Talmudic traditions. A garment possessing rounded ends, or less than four corners, is exempt from the commandment of tzitzit. It has been decided in Halacha that the threads of the tzitzit must be threaded through a hole at each end of the cloth and then multiplied by two, so that eight threads will be produced (one of which is longer than the others and is referred to as shamash). The threads should then be tied in a double, well fastened knot. The shamash is then wound around the other threads and additional knots are tied. There are various customs regarding winding and tying knots, but the two most common call of four groups of 7, 8, 11 and 13 or 5, 6, 5 and 10 windings, with knots tied in between them and at their end. All in all there are five knots in the tzitzit.