Deuteronomy 17
6 At the mouth of two witnesses, or three witnesses, shall he that is worthy of death be put to death; but at the mouth of one witness he shall not be put to death.
7 The hands of the witnesses shall be first upon him to put him to death, and afterward the hands of all the people. So thou shalt put the evil away from among you.
2 Corinthians 13
This is the third time I am coming to you. In the mouth of two or three witnesses shall every word be established.
2 I told you before, and foretell you, as if I were present, the second time; and being absent now I write to them which heretofore have sinned, and to all other, that, if I come again, I will not spare
1 Corinthians 5
3 For I verily, as absent in body, but present in spirit, have judged already, as though I were present, concerning him that hath so done this deed,(ESV - 3 For though absent in body, I am present in spirit; and as if present, I have already pronounced judgment on the one who did such a thing.)
12 For what have I to do to judge them also that are without? do not ye judge them that are within?
13 But them that are without God judgeth. Therefore put away from among yourselves that wicked person.