What is the ruling on one who reads the ahadith which indicate that the parents of the Prophet, peace and blessings be upon him, are among the people of Hellfire, and then says: "I am not convinced by that"?

If the lack of conviction has a permissible Sharia interpretation, such as counteracting evidence with other evidence, then the statement is permissible, like the disagreement among scholars regarding the fate of the Prophet’s parents (peace be upon him). However, if the lack of conviction is merely due to caprice and a rejection of the Prophet’s حديث (saying), then there is a fear of apostasy for its perpetrator, as Allah Almighty says: "It is not for a believing man or a believing woman, when Allah and His Messenger have decided a matter, that they should [thereafter] have any choice about their affair" (Quran 33:36), and His saying: "But no, by your Lord, they will not [truly] believe until they make you, [O Muhammad], judge concerning that over which they dispute among themselves and then find within themselves no discomfort from what you have judged and submit in [full, willing] submission" (Quran 4:65).