Definition: This is a hadeeth in which a narrator in it’s isnad makes the sanad appear to short and closer to the Prophet of Allaah (Sallallahu ‘alayhi wa salam), while in fact, it is longer (i.e. the narrator conceals the identity or misses out 1 or 2 reporters in the isnad). Narrators known to practice tadlis includes; Hasan al-Basree (d.160H), Sulayman al-A’mash (known as the Mushaf).
Types: Ibn Salah (d.643H) Rahimahullaah describes two types of tadlis;
1) Tadlis as-Sanad: This is a chain where a narrator in it reports from his Shaykh (whom he met) or from his contemporary (whom he did not meet) what he did not hear from them, using certain words that give the impression that the narrator heard directly from either one of them.
2) Tadlis ash-Shuyukh: This is a chain where a narrator in it does not mention his Shaykh’s (i.e. immediate authority) identity by names that he is generally known by. Rather, the narrator uses by-names, nicknames, etc, in order not to disclose to the people, the true identity of his Shaykh. Thus, by so doing, the people may think that he is narrating from a totally different person.
Levels: Al- Hafiz ibn Hajar al-Asqalani (d.852H) classified the ‘Mudalliseen’ (i.e. those who practiced tadlis) into five levels;
(a) Those who are known to perform tadlis very rarely e.g. Yahya ibn Sa’eed al-Ansari Rahimahullaah.
(b) Those who perform tadlis but are accepted by the Muhadeetheen, either due to their good reputation and also because of their infrequent performance of tadlis e.g. Sufyan ath-Thawree (d.161H), or due to the fact that they reported from authentic narrators e.g. Sufyan ibn ’Uyaynah (d.197H).
(c) Those who practised tadlis a great deal and were not strict in their performance of it (i.e. they made tadlis of reliable as well as unreliable narrators) e.g. Abul-Zubayr al-Makki. In this case, the Muhadeethoon have accepted from these narrators such ahadeeth which were narrated with a clear mention that they heard these ahadeeth direct from their immediate authorities.
(d) Those who practice tadlis a great deal but mostly of weak narrators e.g. Baqiyyah ibn al-Waleed. In this case, the Muhadeetheen have rejected the ahadeeth narrated by this level of Mudalliseen, except, if they clearly admit to hearing the ahadeeth directly from their immediate authorities.
(e) Those who perform tadlis but are known to be weak due to other defects such as; lying, innovating, etc. e.g. ’Abdullaah ibn Luhayah. In this case, any ahadeeth narrated from them is completely rejected even if they admit hearing them directly from their immediate authorities.
A hadeeth that is narrated by a person who is known to be a Mudallis is totally rejected, except in certain cases;
- The narrator who is Mudallis must be known to be trustworthy and reliable. Furthermore, he must state that he heard the hadeeth directly from his Shaykh.
- A trustworthy and reliable Mudallis narrates the hadeeth, it is written in the books known to be authentic (e.g. Saheeh al-Bukhari) and there is Ijma (Consensus/Agreement) that the hadeeth is Saheeh.
 At-Taqyid wa ’l-Idah Sharh Muqaddimah ibn As-Salah by Zaynad-Deen Al-Iraqi (d.806H).
 Al-Iraqi (d.806H) Rahimahullaah adds a third type of tadlis, called Tadlis at-Taswiyyah: This is an isnad where there is a weak narrator in between 2 trustworthy narrators (i.e. a weak narrator transmits from a reliable narrator and then another reliable narrator transmits from the weak narrator). So the narrator of this isnad omits the intermediate weak narrator, leaving the isnad apparently consisting of reliable narrators. At-Taqyid wa ’l-Idah Sharh Muqaddimah ibn as-Salah by Al-Iraqi (d.806H)pg. 96
 Taqabat al-Mudalliseen by Ibn Hajar Al-Asqalani (d.852H) pg.7f