Hadith and Sunnah are generally taken as synonymous terms. This is not a correct impression. The words Hadith and Sunnah have entirely different connotations, and each one holds a different status in the Shari′ah. If we assign the same meaning to both the terms, it would create a lot of complications. For a proper understanding of the science of Hadith, therefore, it is necessary to know precisely the difference between Hadith and Sunnah.
Hadith implies the narration of a saying, or of an act, or of an approval (Taswib) of the Prophet (sws), irrespective of whether the matter is authenticated or still disputed. The Muhaddithin (the scholars of Hadith) use the word Taqrir to express Taswib. It implies that while doing something in the presence of the Prophet (sws), a Muslim acted in a particular manner and the Prophet (sws) observed it and did not disapprove it. In this way, that person received the tacit approval of the Prophet (sws) regarding that particular action.
The Muhaddithin employ the term, Khabar for Hadith. A Khabar bears the possibility of being either right or wrong. In other words, the Muhaddithin believe that a Khabar may be authentic or it may be false. On this account, the Ahadith (plural of Hadith) are also termed as Zanni (presumptive or undefined). This means that a Hadith could be anything ranging from Sahih to Hasan, Da′if, Mawdu′, or Maqlub1
Therefore each one of these categories should be treated on its own merits.