These two conditions of ṣaḥīḥ li-dhātihi apply to every narrator:
• Every narrator is ʿādil.
• Every narrator is tāmm al-ḍabṭ.
It is not enough for only one narrator to have these qualities; they are required of each narrator in the sanad.1
1. Sanad (سند): the sequence of narrators through whom a Hadith was received.