Islam / Sharia /
An isnad was effectively the quality proof of a tradition, as it by its transmitters could be tested, thereby setting the validity of the tradition. The testing of the isnad was a central technique in the systemizing of the traditions, having the hadith collections as its product.
An early categorization of the traditions were to arrange them according to which companion of Muhammad they were attributed. The companion was in this case called musnad, a term with the same root as isnad, s-n-d. The musnad may be said to be the first link in the isnad.
In hadith collections the isnad is usually omitted, although most traditions are introduced with naming the musnad. It then follows this pattern: "Abdullah reported that the Messenger of God (Peace and Blessings be upon him) said" followed by the actual hadith.
The full isnad, usually included in the original hadith collections, would normally follow this pattern: "I have been told by [A] on the authority of [B], on the authority of [C], on the authority of [D], that the Messenger of God said..."
When evaluating the quality of an isnad, the hadith collectors used several techniques. They judged whether the persons listed in the isnad actually could have transmitted the tradition, if it was likely that they had met, whether the circumstances had allowed for proper transmission, if the people in the isnad were considered trustworthy and so on. In many respects, the evaluation of isnads had great similarities with modern historical research, though of course its possibilities were limited from the special case of verbal traditions.
Also the traditions were investigated, asking whether the content was logical, in correspondence with other traditions, were the words likely to have been uttered by Muhammad or the others in question?
Despite the diligence of the hadith collectors, modern scholars will regard the entire hadith collections with some suspicion, largely from the fact that there are important differences between the 6 which dominate Muslim traditions.
It lies in the nature of the isnad that it easily could be falsified by anyone knowing the Muslim past well. This was a challenge well-known to the hadith collectors, it may even be held as the main reason for collecting the traditions and testing their quality. Still, the chances for false traditions to have become part of orthodox Islam are high.