BahÃ ` u 'll Ã h had written that ` Abdu ` l-Bah Ã had special powers , and that God would make sure that if ` Abdu ` l-Bah Ã explained anything that BahÃ ` u 'll Ã h said , then the BahÃ ' Ã s should believe that explanation .
BahÃ ` u 'll Ã h 's KitÃ b-i-Aqdas and The Will and Testament of ` Abdu ` l-Bah Ã are foundational documents of the BahÃ ' Ã administrative order . BahÃ ` u 'll Ã h established the elected Universal House of Justice , and ` Abdu ` l-Bah Ã established the appointed hereditary Guardianship and clarified the relationship between the two institutions .