BahÃ ` u 'll Ã h wrote many books and letters , and ` Abdu ` l-Bah Ã ( whose name means `` Servant of Glory '' ) also wrote many books and letters which BahÃ ' Ã s see as special . ` AbbÃ s Effendi was BahÃ ` u 'll Ã h 's eldest son , known by the title of ` Abdu ` l-Bah Ã ( Servant of BahÃ ) .