His mother, Umaimah bint Abdul Muttalib, was one of the paternal aunts of the Holy Prophet (sa). Thus, he was a cousin of the Holy Prophet (sa). He had accepted Islam prior to the Holy Prophet (sa) going into Darul Arqam.
(Usdul Ghaaba, Vol. 3, p.89, Abdullah bin Jahsh, Darul-Fikr, 2003, Beirut).