On the testimony of two or three witnesses a person is to be put to death, but no one is to be put to death on the testimony of only one witness. (Deuteronomy 17:6)
One witness is not enough to convict anyone accused of any crime or offense they may have committed. A matter must be established by the testimony of two or three witnesses. (Deuteronomy 19:15)
When they returned to Joshua, they said, “Not all the army will have to go up against Ai. Send two or three thousand men to take it and do not weary the whole army, for only a few people live there.” (Joshua 7:3)
part of a cake of pressed figs and two cakes of raisins. He ate and was revived, for he had not eaten any food or drunk any water for three days and three nights. (1 Samuel 30:12)
He looked up at the window and called out, “Who is on my side? Who?” Two or three eunuchs looked down at him. (2 Kings 9:32)
Yet some gleanings will remain, as when an olive tree is beaten, leaving two or three olives on the topmost branches, four or five on the fruitful boughs,” declares the Lord, the God of Israel. (Isaiah 17:6)
But if they will not listen, take one or two others along, so that ‘every matter may be established by the testimony of two or three witnesses.’ (Matthew 18:16)
For where two or three gather in my name, there am I with them.” (Matthew 18:20)
If anyone speaks in a tongue, two—or at the most three—should speak, one at a time, and someone must interpret. (1 Corinthians 14:27)
Two or three prophets should speak, and the others should weigh carefully what is said. (1 Corinthians 14:29)
This will be my third visit to you. “Every matter must be established by the testimony of two or three witnesses.” (2 Corinthians 13:1)
Do not entertain an accusation against an elder unless it is brought by two or three witnesses. (1 Timothy 5:19)
Anyone who rejected the law of Moses died without mercy on the testimony of two or three witnesses. (Hebrews 10:28)
All of the above are from a biblegateway.com search for "two or three" in the New International Version (NIV).
The Bible is full of wisdom, and this is some of that wisdom.
God holds himself to this standard.
All glory to Him.