What is the meaning of the word Tadlis and Mudallis with respect to the science of Hadith and also the position of the status or grade of Hadith whose one or more of its transmitter is considered to be Mudallis .
A Mudallis is basically one who has the habit of omitting or changing the name of his teacher in the chain.
This action is called Tadlis.
If he has the habit of omitting his teacher [as opposed to merely changing his name], then his narrations will only be accepted if he reports the narration using words that denote him acquiring the narration directly from the source he quotes (التصريح بالسماع).
If he uses the word ‘an (عن) when reporting, the chain will be considered weak.
(Refer: Tadribur Rawi, vol. 3 pg. 239-252-263.)
And Allah Ta’ala Knows best,
Answered by: Moulana Muhammad Abasoomar
This answer was collected from HadithAnswers.com. The answers were either answered or checked by Moulana Haroon Abasoomar (rahimahullah) who was a Shaykhul Hadith in South Africa, or by his son, Moulana Muhammad Abasoomer (hafizahullah), who is a Hadith specialist.