What is the ruling on one who intentionally insults one of the Companions?

The Companions of the Messenger of Allah are the best of the Ummah, and Allah and His Messenger have praised them. Whoever curses them is a denier of Allah and His Messenger, and proof must be established against him. If he repents, then Allah is Oft-Forgiving, Most Merciful. But if he persists, he is a disbeliever, misguided, and misguiding others. Al-Khallal narrated that Imam Ahmad was asked about someone who curses Abu Bakr, Umar, and Aisha, and he said: "I do not consider him to be on Islam." As for cursing a Companion with a description that does not impugn his religiosity or integrity (such as describing him as stingy or cowardly), or cursing a Companion whose virtues have not been established by widely transmitted texts, such cursing does not constitute disbelief. However, it necessitates discipline and chastisement.