Judaism prohibits shaving with a razor on the basis of a rabbinic interpretation of Leviticus 19:27, which states, "You shall not round off the side-growth on your head, or destroy the side-growth of your beard." The Mishnah interprets this as a prohibition on using a razor on the beard. This prohibition is further expanded upon in kabbalistic literature. The halakhic prohibition applies to shaving off the pe'ot (sidelocks) and corners of the beard by means of a razor.
For more see here
