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:
1Pet. 2:4 And coming to Him as to a living stone which has been rejected by men, but is choice and precious in the sight of God,
1Pet. 2:5 you also, as living stones, are being built up as a spiritual house for a holy priesthood, to offer up spiritual sacrifices acceptable to God through Jesus Christ.
1Pet. 2:9 But you are A CHOSEN RACE, A royal PRIESTHOOD, A HOLY NATION, A PEOPLE FOR God’s OWN POSSESSION, so that you may proclaim the excellencies of Him who has called you out of darkness into His marvelous light;
1Pet. 2:10 for you once were NOT A PEOPLE, but now you are THE PEOPLE OF GOD; you had NOT RECEIVED MERCY, but now you have RECEIVED MERCY.
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: