Tadlis refers to the case where the narrator uses an ambiguous term which does not tell us if he heard the hadith directly from the one on whose authority he has narrated it. For example, a Mu'an'an hadith is one in which the narrator has used the term 'an, e.g., 'an Muhammad meaning "on the authority of Muhammad." He could have heard the hadith directly from Muhammad or from someone else, possibly a fabricator of hadith. In both cases, it is permissible to use the term 'an.Muhammad ibn Ishaq is one such narrator, who used to commit Tadlis. If he narrated the hadith in such a way that it is clear that he heard it directly from the one on whose authority he is relating it, then his hadith is acceptable. The latter narrator is considered weak when he relates in Mu'an'an form because of his reputation as one who commited Tadlis.