Shaykh al-Islām—may Allah have mercy on him—said:

A report may be known to be true, known to be false, or neither.

The first category:

Reports known to be true. This is generally established through accompanying evidence: either transmission by people whom reason cannot conceive of deliberately lying or colluding in falsehood, or other corroborating circumstances surrounding the report. This knowledge is of two kinds. One is immediate knowledge, requiring no effort on the mind’s part to acquire it, and … (1)

This category includes reports that the Muslim community has accepted and unanimously acted upon, or relied upon in practice. For had such a report been false, [they would not have acted upon it, since it is impossible for] (2) them to agree upon error. It is … (3)

It does not detract from this that the report does not, by itself, yield certain knowledge. This resembles a ruling established by consensus but based on analogy, independent juristic reasoning, and considered opinion. And … (4) the disputed report is, in itself, only probable; how, then, can it become certain? Yet he has not understood that probability and certainty are qualities of the investigator’s belief, according to the evidence apparent to him; the report itself has acquired no new attribute.

The second category:

Reports known to be false, or refuted by sound reason, the Book, or