Deuteronomy 19:15
A lone witness is not sufficient to establish any wrongdoing or sin against a man, regardless of what offense he may have committed. A matter must be established by the testimony of two or three witnesses.
General
Deuteronomy 17:6
On the testimony of two or three witnesses a man shall be put to death, but he shall not be executed on the testimony of a lone witness.
Numbers 35:30
If anyone kills a person, the murderer is to be put to death on the testimony of the witnesses. But no one is to be put to death based on the testimony of a lone witness.
1 Kings 21:10, 13
But seat two scoundrels opposite him and have them testify, ‘You have cursed both God and the king!’ Then take him out and stone him to death.” ... And the two scoundrels came in and sat opposite Naboth, and these men testified against him before the people, saying, “Naboth has cursed both God and the king!” So they took him outside the city and stoned him to death.
Matthew 18:16
But if he 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 26:60-61
But they did not find any, though many false witnesses came forward. Finally two came forward and declared, “This man said, ‘I am able to destroy the temple of God and rebuild it in three days.’”
John 8:17
Even in your own Law it is written that the testimony of two men is valid.
2 Corinthians 13:1
This is the third time I am coming to you. “Every matter must be established by the testimony of two or three witnesses.”
1 Timothy 5:19
Do not entertain an accusation against an elder, except on the testimony of two or three witnesses.
Hebrews 10:28
Anyone who rejected the law of Moses died without mercy on the testimony of two or three witnesses.
Revelation 11:3-7
And I will empower my two witnesses, and they will prophesy for 1,260 days, clothed in sackcloth.” These witnesses are the two olive trees and the two lampstands that stand before the Lord of the earth. If anyone wants to harm them, fire proceeds from their mouths and devours their enemies. In this way, anyone who wants to harm them must be killed. These witnesses have power to shut the sky so that no rain will fall during the days of their prophecy, and power to turn the waters into blood and to strike the earth with every kind of plague as often as they wish. When the two witnesses have finished their testimony, the beast that comes up from the Abyss will wage war with them, and will overpower and kill them.