in taqrib al-nawawi [#20] mudraj [addendum in the text/chain] has categories: the first: mudraj [addendum] in the hadith of the Prophet sallAllahu alayhi wa sallam, such that a narrator mentions after [his narration,] something which is his own speech or the speech of others [not the text of the hadith] - and then it is narrated thereafter together [without distinguishing] and it appears as if it is [portion] of the hadith. the second: the narrator has two different texts, with two different chains and he narrates them both, with one of the chains. the third: that he hears a hadith from a group, [narrators among who have] varying/different texts and chains and he narrates from all of them without making any distinction. all of this is Haram - khatib [al-baghdadi] has written a book* on this which deals with this issue adequately. *al-faSl li'l waSl al-mudraj fi'n naql. suyuti in his tadrib al-rawi says: (p.137) ibn al-sam'ani said: "whoever knowingly and deliberately [ta'ammada] adds into the [text/sanad of the] hadith has lost his status as a trustworthy narrator [saqiT al-adalah]; and he is a tamperer and is among the liars." as for me [suyuti] i consider the inadvertent addendum [idraj] for the explanation of arcane words/idioms [gharib] is not impermissible. it is therefore zuhri did so, and so also did many other scholars.