What is the ruling on one who denies hadiths mentioned in books of Tafsir (exegesis) if they are not found in the six major hadith collections, and what is the ruling on one who only accepts the Two Sahihs (Bukhari and Muslim) to the exclusion of other hadiths, and what is the proof for that?

The authenticity and acceptance of hadiths depend on the soundness of their chains of transmission (isnads) and the ruling of acceptance by the imams of hadith, and this is not limited to the Two Sahihs (Bukhari and Muslim) or the Six Books. Bukhari and Muslim did not encompass all authentic hadiths, and they left out many of them, as they themselves stated. Authentic hadiths beyond the Two Sahihs are known through the explicit statements of reliable imams affirming their authenticity, or from specialized compilations of authentic hadiths such as Sahih Ibn Khuzaymah, Sahih Ibn Hibban, and Al-Mustadrak by Al-Hakim. The objection that whatever is not in the Two Sahihs is not authentic is a false claim. Indeed, the huffaz (hadith masters) criticized anyone who thought that Muslim had restricted authenticity to his collection. Rather, whatever is authentically reported from the Prophet - peace be upon him - is a proof, regardless of its source.