Significance Of Khabr-e-Ahad
“If saying of the prophet proves to be authentic and correct, it is kufr to ignore it.” Well, that’s a big “if”. How do you prove it to be authentic and correct? can you cite an example of such a Hadith, which if ignored leads to “kufr”? Also, your opinion on authenticity of a certain narration may differ than mine, so please slow down on the kufr verdict.
What Irfan sahab stated above has nothing to do with the subjectivity involved in determining the authenticity of a narration. If someone puts in sincere effort and concludes a narration to be true, then denying it is certainly kufr.