Muadh ibn Jabal one of the companions who accepted Islam from Madina, from the tribe of Khazraj. He was one who the Prophet Sallallahu Alayhi WaSallam gave special responsiblities, especially in the area of dawah. He is well known for the hadith of the call to Tawheed where the Prophet Sallallahu Alayhi WaSallam sent him to Yemen as the governer, judge, teacher of Yemen and told him that you’re coming to a people from the people of the book and the first thing that you should call them to is the oneness, unique oneness of Allah. If they accept that, then inform them that Allah has made obligatory on them five daily prayers and so on and so forth.