Hi since you are speaking about the Bible: If he or she is in your Christian Church then
When elders learn about serious wrongdoing, they approach the individual involved to give needed help and correction. It is the elders’ responsibility to judge such ones inside the Christian congregation. Keeping a close watch on its spiritual condition, they assist and admonish anyone who is taking an unwise or wrong step.—1 Corinthians 5:12, 13; 2 Timothy 4:2; 1 Peter 5:1, 2.
But what if you are not an elder and you come to know about some serious wrongdoing on the part of another Christian? Guidelines are found in the Law that God gave to the nation of Israel. The Law stated that if a person was a witness to apostate acts, sedition, murder, or certain other serious crimes, it was his responsibility to report it and to testify to what he knew. Leviticus 5:1 states: “Now in case a person sins in that he has heard public cursing and he is a witness or he has seen it or has come to know of it, if he does not report it, then he must answer for his error.”—Compare Deuteronomy 13:6-8; Esther 6:2; Proverbs 29:24.
Though not under the Mosaic Law, Christians today can be guided by the principles behind it. (Psalm 19:7, 8) So if you learn about the serious wrongdoing of a fellow Christian, what should you do?
First of all, it is important that there is valid reason to believe that serious wrongdoing has really occurred. “Do not become a witness against your fellowman without grounds,” stated the wise man. “Then you would have to be foolish with your lips.”—Proverbs 24:28.
You may decide to go directly to the elders. It is not wrong to do so. Usually, however, the most loving course is to approach the person involved. Perhaps the facts are not as they appear to be. Or perhaps the situation is already being handled by the elders. Calmly discuss the matter with the person. If there remains reason to believe that a serious wrong has been committed, encourage him or her to approach the elders for help, and explain the wisdom of doing so. Do not talk to others about the matter, for that would be gossip.
If the person does not report to the elders within a reasonable period of time, then you should. One or two elders will then discuss the matter with the accused. The elders need to “search and investigate and inquire thoroughly” to see if wrong has been done. If it has, they will handle the case according to Scriptural guidelines.—Deuteronomy 13:12-14.
At least two witnesses are required to establish a charge of wrongdoing. (John 8:17; Hebrews 10:28) If the person denies the charge and your testimony is the only one, the matter will be left in God’s hands. (1 Timothy 5:19, 24, 25) This is done in the knowledge that all things are “openly exposed” to God and that if the person is guilty, eventually his sins will “catch up” with him.—Hebrews 4:13; Numbers 32:23. Hope this helps.