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.
2 Corinthians 13:1
1 This is the third time I am coming to visit you. By the testimony of two or three witnesses every matter will be established. 2 I said before when I was present the second time and now, though absent, I say again to those who sinned previously and to all the rest, that if I come again, I will not spare anyone, 3 since you are demanding proof that Christ is speaking through me. He is not weak toward you but is powerful among you. 4 For indeed he was crucified by reason of weakness, but he lives because of God’s power. For we also are weak in him, but we will live together with him, because of God’s power toward you. 5 Put yourselves to the test to see if you are in the faith; examine yourselves! Or do you not recognize regarding yourselves that Jesus Christ is in you—unless, indeed, you fail the test!
Notes and References
"... In addition to Matt 18:15-20, we find Deuteronomy 19:13 alluded to in 2 Corinthians 13:1, where Paul tells the Corinthians that any charges they make against one another 'must be sustained by the evidence of two or three witnesses.' And in 1 Timothy 5:19 there is this: 'Never accept any accusation against an elder except on the evidence of two or three witnesses.' Once again, then, Matthew appears to stand within a tradition. That is, Matthew 18:15-20 not only takes up a Jewish tradition based upon Leviticus 19:17-18, it also is in harmony with the application of Deuteronomy 19:15 found in 2 Corinthians 13:1 and 1 Timothy 5:19 ..."
Allison, Dale C. Scriptural Allusions in the New Testament: Light from the Dead Sea Scrolls (p. 28) Wipf & Stock Publishers, 2019