Is everything mentioned in the authentic prophetic hadith collections considered sound, not permissible for discussion by scholars in modern times, or does that contradict the noble verse: "And if it were from other than Allah, they would have found within it much contradiction"?

Allah Almighty has only ordained infallibility for His Book, the Qur'an, which has been transmitted to us through continuous, mass transmission (tawatur), making its authenticity definitive (qat'i al-thubut). As for the books of the Prophet's Sunnah, some of what they contain has been transmitted through tawatur, making its authenticity definitive, while other parts have been transmitted through individual narrations (ahad), making their authenticity conjectural (dhanni al-thubut).

No scholar has ever said that it is impermissible to critique the narrations in the books of the Sunnah, provided that this is done according to the jurisprudential guidelines and scientific principles established by Hadith scholars. The aforementioned verse, "Then do they not reflect upon the Qur'an? If it had been from [any] other than Allah, they would have found within it much inconsistency," (4:82) was revealed concerning the Noble Qur'an. The Sunnah, though inspired by Allah Almighty, clarifies and explains the Qur'an. What comes from other than Allah contains much inconsistency. However, the Book and the authentic Sunnah contain no inconsistency or contradiction; rather, differences arise in their understanding.