Deuteronomy 19:15
13 You must not pity him, but purge from Israel the guilt of shedding innocent blood, so that it may go well with you. 14 You must not move your neighbor’s boundary marker,28 which will have been defined in the inheritance you will obtain in the land the Lord your God is giving you. 15 A single witness may not testify against another person for any trespass or sin that he commits. A matter may be legally established only on the testimony of two or three witnesses. 16 If a false witness testifies against another person and accuses him of a crime, 17 then both parties to the controversy must stand before the Lord, that is, before the priests and judges who will be in office in those days.
Matthew 18:16
15 “If your brother sins, go and show him his fault when the two of you are alone. If he listens to you, you have regained your brother. 16 But if he does not listen, take one or two others with you, so that at the testimony of two or three witnesses every matter may be established. 17 If he refuses to listen to them, tell it to the church. If he refuses to listen to the church, treat him like a Gentile or a tax collector. 18 “I tell you the truth, whatever you bind on earth will have been bound in heaven, and whatever you release on earth will have been released in heaven. 19 Again, I tell you the truth, if two of you on earth agree about whatever you ask, my Father in heaven will do it for you.
Notes and References
"... Matthew 18 forms the fourth of the five major blocks of sermonic material that this Gospel groups together (the others are chaps. 5–7; 10; 13; 23–25). Jesus is speaking privately to his disciples about the themes of humility and forgiveness. Matthew 18:15–18 forms the well-known passage on church discipline. Here a procedure is outlined not just for confronting flagrant sinners, but for dealing with any unresolved grievances ... Together, 18:15–20 provide an important contextual qualification, as do 18:23–35, to the apparently unlimited forgiveness that 18:21–22 enjoin. As the parallel in Luke 17:3–4 also demonstrates, that forgiveness is applicable only when genuine repentance has occurred. When it has, though, people truly forgiven by God will forgive others. Deuteronomy 19:15 is cited again in 2 Corinthians 13:1, alluded to in 1 Timothy 5:19, and its principle seems to lie behind the actions taken in Matthew 26:59–61; and John 8:17 (where this law appears to be paraphrased); Hebrews 6:18; Revelation 11:3 ..."
Beale, G. K., and D. A. Carson Commentary on the New Testament Use of the Old Testament (p. 178) Baker Academic, 2007