The Hadith is the record of the sayings of Prophet Muhammad (pbuh). The sayings and conduct of Prophet Muhammad (pbuh) constitute the Sunnah.The Hadith has come to supplement the Quran as a source of the Islamic religious law.Isnad means the chain of transmitters to that Hadith.
The scholars of the Hadith literature divided the Traditions into categories according to the degree of authenticity and reliability, each category had to meet certain criteria.
The categories are as follows:
1. Sahih: The genuine Traditions, the authentic ones.
2. Moothaq: Almost like the Sahih but the narration is not as strong as those of the Sahih.
3. Hasan: The fair Traditions although inferior in matter of authenticity.
4. Dha'eef: The weak Traditions which are not so reliable.
In Shari'ah (Islamic Constitution) deeds and actions are divided into five classes:
1. Wajib: An obligatory duty.
2. Mustahab: An action which is rewarded.
3. Mubah: An action which is permitted but legally is indifferent.
4. Makruh: An action which is disapproved.
5. Haram: An action which is forbidden.