Which passage in the Torah, Old Testament or New Testament said Christians must confess their sin to a Priest, as in Catholicism?
There is no instruction in the Bible requiring confession to a priest. In fact, there is no such thing as a position of “priest” for Christians. According to the Bible, ALL Christians are priests:
Peter says to the church that you (i.e., all believers) are part of a priesthood. We are all priests (i.e., ministers) to each other and the world. There is no such thing as a special position called “priest.” That teaching is a heresy of the Catholic religion.
For the same reason, there is no requirement to confess sins to a specific person called a “priest.” This is also a false teaching of the Catholic religion. The Bible says that we are to confess our sins to one another, because we are all priests: