The authenticity of a hadith, which is a saying or action attributed to the Prophet Muhammad, may be doubted if it contradicts a clear teaching of the Quran, which is the central holy book of Islam. Additionally, if the wording of the hadith is too similar to the Quranic text, it could also be questioned as to whether it is a genuine statement from the Prophet. Similarly, if the hadith is no longer than a verse of the Quran, it could be considered too brief and therefore potentially not authentic. Finally, the reliability of the narrator is also a factor, and if the person who transmitted the hadith was not from the city of Makkah, it may raise doubts about the accuracy of the hadith.