Hadith of the Ark ""perished whoever turned away from it"" also comes along." And in his another book, Al-Heithami indicates this hadith as authentic (sahih). According to Dahlan, the authenticity of this hadith is confirmed by different sources. The hadith implies the absolute priority of "Ahl al-Bayt" to all others, otherwise Muhammad would have forbidden to follow them. According to Shia scholars, the only path to salvation is by following the "Ahl al-Bayt", so they must be infallible ("Ma'sum"), otherwise they will mislead their followers. If they are infallible, they must be Imam definitely. According to this hadith, they are the criterion of distinguishing
Introduction to the Science of Hadith adding six terms in the process). The first pertains to the "matn" (text) of the hadith and its three divisions and 30 types. The three divisions are "ṣaḥīḥ", "ḥasan", and "ḍa`īf". The thirty types include those mentioned in hadith terminology and others. The second deals with the "isnād" (chain of narration) and comprises 11 types. These types generally fall within the discipline of biographical evaluation. The third category includes six types: the qualifications necessary for conveying hadith, the manners in which they are transmitted, the transcription of hadith, and the etiquette of the narrator and of the student. The fourth