Tzizit String TeKhelet - Blue String - Avodat Yad

"Speak to the Children of Israel and bid them that they make fringes on the corners of their garments throughout their generations, and that they put upon the fringe of each corner a thread of blue (tekhelet). And it shall be for you as a fringe, that you may look upon it and remember all the commandments of G-d, and do them..." (Numbers 15:38-39)