Discuss the contribution of Imam at-Tirmidhi to the development of science of Hadith.

Abu ‘Isa Muhammad ibn ‘Isa at-Tirmidhi (c. 824-892 C.E.) was one of the six great compilers of Hadith. He was born in Tirmidh and travelled widely in search of Hadith, studying under Imam al-Bukhari and others. His contributions to the science of Hadith include:

1. Compilation of al-Jami‘ (Sunan at-Tirmidhi), one of the six authentic Hadith collections (al-Kutub as-Sittah), arranged by chapters of jurisprudence for ease of reference.
2. Grading of Hadith. He was the first to classify traditions systematically as sahih (sound), hasan (good), gharib (rare) and da‘if (weak), and he popularised the term hasan as a distinct grade.
3. Comment on the status of each Hadith. After most traditions he stated its degree of authenticity, the opinions of jurists on it, and which scholars acted upon it, thereby linking Hadith to Fiqh.
4. Preservation of the chains of narration (Isnad). He carefully recorded the narrators and defects of narrations, aiding the critical evaluation of reports.
5. Work on the narrators. He wrote Kitab al-‘Ilal on the hidden defects of Hadith and discussed the reliability of transmitters.
6. A model for later scholars. His method of combining narration, grading and juristic discussion became a standard reference for students of Hadith.
7. Wide circulation and teaching. His collection spread the authentic sayings of the Prophet and preserved the Sunnah for the Ummah.

Through these efforts, Imam at-Tirmidhi greatly advanced the science of Hadith criticism and preserved the Prophetic tradition.