Tadlis is a mode of transmission in which a narrator uses wording that may suggest direct receipt although that particular report was not heard directly from the person cited. The Arabic term carries a sense of concealing a relevant aspect of the transaction.
«عَنْ فُلَانٍ»
From so-and-so.
The formula “ʿan” does not by itself prove tadlis; genuine connected narration frequently uses it. The concern arises when a known narrator's practice of tadlis, the specific route, and evidence about hearing make a concealed intermediary plausible.
Consequently, the presence of “ʿan” alone is not grounds to accuse a narrator of tadlis. His biography, contact with the named teacher, and parallel routes must be examined.