What is the ruling on one who denies an authentic hadith firmly established in Sahih al-Bukhari or Muslim?

If a hadith meets the conditions of authenticity and is not abrogated, then it is obligatory to accept it and act upon it. Denying it is considered stubbornness and obstinacy. Some scholars have gone so far as to declare someone who denies the authenticity of a hadith, while knowing it to be authentically narrated from the Prophet, peace and blessings be upon him, to be a disbeliever. As for denying the content of a hadith, if it concerns a matter known by necessity to be part of the religion, then the one who denies it is a disbeliever; otherwise, they are not. It is obligatory to accept any hadith authentically narrated from the Prophet, peace and blessings be upon him, and to act upon its implications, whether it is an Ahad (single-chained) or Mutawatir (mass-narrated) hadith.