The biblical standard of BY TWO OR MORE WITNESSES TO RATIFY DOCTRINE).
'One witness doth not rise against a man for any iniquity, and for any sin, in any sin which he sinneth; by the mouth of two witnesses, or by the mouth of three witnesses, is a thing established - Deuteronomy 19:15.
But if he will not hear thee, then take with thee one or two more, that in the mouth of two or three witnesses every word may be established - Matthew 18:16.
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 - 2 Corinthians 13:1.