What is the Shar'i criterion for conveying speech, and is Ibn Mas'ud's informing the Messenger (PBUH) of the man's statement, "This is a division by which the face of Allah was not intended," considered backbiting?

What Ibn Mas'ud did—in informing the Prophet, peace and blessings be upon him, about the man's words—is not forbidden backbiting (namimah). Rather, it is an act of preventing harm and offering sincere advice for the sake of Allah, His Messenger, and the believers. Backbiting is not forbidden if the نقل (conveying) and إفشاء (disclosure) of speech involves a benefit or averts harm from Muslims that cannot be repelled except by such means.