«مُؤْمِنًا بِهِ»
This qualification requires faith in the Prophet ﷺ at the relevant meeting. Merely seeing or speaking with him while not believing in him does not establish Companion status.
Case 1: A person met him as an unbeliever, accepted Islam later, and had no further encounter during the Prophet’s life. That earlier meeting does not, on its own, meet the definition.
Case 2: The person accepted Islam, then met him again while believing, and died a Muslim. The qualifying encounter is now present.
This distinction matters because living during the Prophetic period, having incidental proximity, and meeting him as a believer do not amount to the same technical relationship.