When is it permissible to declare people disbelievers or open sinners?

Question:
Shaykh Salih, some people have been lax in declaring many people disbelievers or open sinners without knowledge or proof. Is there any guidance at the end of this lesson?

Answer:
It is not permissible to declare people disbelievers or open sinners except for those who deserve it by committing one of the nullifiers of Islam, in which case they are declared disbelievers. If a person commits a major sin, such as unlawful sexual intercourse, theft, or drinking intoxicants, and does not repent, he is declared an open sinner. These are scholarly matters; disbelief and open sinfulness are scholarly terms that are not permissible to apply except to those who deserve them. Yes.