When is the addition of a trustworthy narrator accepted?

The questioner : Well, Shaykh, there is another question: When is the addition of a trustworthy narrator accepted?

The Shaykh : There is no doubt that this is a matter of ambiguity for some people, especially those who have recently become attached to this science. It is known that one of the conditions of an authentic hadith is that it not be anomalous. Anomalousness often accompanies an addition, and often it does not. Sometimes the addition is accepted, and sometimes it is rejected. If the addition is from a trustworthy narrator to a narrator of equal standing, it is accepted. However, if the addition is from a trustworthy narrator to one who is more trustworthy, or to one who has more narrators, then the addition is rejected, and this is anomalousness. With this detail, the question regarding the addition is answered.