What is the science of Hadith? How were hadiths classified and graded? Is there any authentic book on this?

 The science of hadith, also known as musthalah al-hadith, is the study of the various classifications and grading systems of hadith. It is a complex and challenging field of study, but it is essential for understanding the hadith literature and for distinguishing between authentic and inauthentic hadith.

There are many different classifications and grading systems of hadith, but some of the most common include:

• Classification by number of narrators:  Hadith can be classified according to the number of narrators at each level of the chain of transmission (isnad). Hadith that are narrated by a large number of narrators are considered to be more authentic than hadith that are narrated by a small number of narrators.
• Classification by strength of the chain of transmission:  Hadith can also be classified according to the strength of the chain of transmission. Hadith that have a complete and unbroken chain of transmission, with all of the narrators being reliable and trustworthy, are considered to be more authentic than hadith that have a weak or incomplete chain of transmission.
• Classification by the text of the hadith:  Hadith can also be classified according to the text of the hadith itself. Hadith that are consistent with the Quran and other well-established hadith are considered to be more authentic than hadith that contradict the Quran or other well-established hadith.

There are many authentic books on the science of hadith. Some of the most well-known books include:

• Muqaddimah Sahih al-Bukhari  by Imam Bukhari
• Nukhbat al-Fikar  by Imam Ibn Hajar al-Asqalani
• 'Ulum al-Hadith  by Imam al-Shatibi
• Al-Itqan fi `Ulum al-Quran  by Imam al-Suyuti

These books provide a comprehensive overview of the science of hadith, including the various classifications and grading systems of hadith. They are essential reading for anyone who wants to understand the hadith literature and to distinguish between authentic and inauthentic hadith.

In addition to the books mentioned above, there are many other authentic books on the science of hadith. These books are available in both Arabic and English. Some of these books are more comprehensive than others, and some are more focused on specific aspects of the science of hadith.

If you are interested in learning more about the science of hadith, I recommend that you start by reading one of the books mentioned above. Once you have a basic understanding of the science of hadith, you can then explore other books and articles on the subject.