If there is a difference by ziyādah (addition of a narrator) at the end of the sanad, and the person who does not narrate with the ziyādah is of a higher level than the person narrating with the ziyādah, then this is termed al-mazīd fī muttaṣil al-asānīd.The condition of accepting the ziyādah is that the ziyādah occurs with clarification that the ziyādah was heard directly at that place.[1] If this is not the case, then whenever there is an ziyādah, we give preference to this over the narration with the ziyādah.
[1] Such as one saying سمعت, حدثنا, or أخبرنا meaning “I heard”, “It was related to me” or “I was informed”.
