Numbers 15:39

All the commandments] The Rabbis enumerated 613 commandments in the Law. It so happens that the numerical value of the letters in the Hebrew word for fringe (zisith) is exactly 600. To make this number up to 613 the tassel was made of eight threads with five knots. In this way each tassel represented the 613 commandments, and the wearing of it was said to be of equal merit with the keeping of the whole law. This is a good example of Rabbinical interpretation and of external scrupulosity. Go a whoring] see on Exodus 34:15.