Is it considered an act of disbelief (kufr) for someone to reject authentic hadiths found in "Sahih al-Bukhari, Sahih Muslim, and other collections" under the pretext that they contradict the Qur'an?

The Prophetic Sunnah is the second source of legislation, and Allah has made it obligatory to completely submit to the words of the Prophet, peace and blessings be upon him. Whoever denies the authority of the Sunnah or disbelieves a Hadith of the Prophet, peace and blessings be upon him, while knowing it is from his words, has committed an act of disbelief. As for one who rejects a Hadith denying it to be from the words of the Prophet, peace and blessings be upon him, this implies a complete contradiction between the Hadith and the Holy Qur’an, or the presence of a weak chain of transmission. The one who rejects it must be qualified for research and Ijtihad; otherwise, he falls into great danger. Thus, whoever rejects a Hadith of the Messenger of Allah, peace and blessings be upon him, is on the brink of destruction.