Al-Hakim bi-Amr Allah
Subsequent Fatimid imams and caliphs and Ismaili dai's have relied on Da'a'im-ul-Islam'. The 16th Fatimid imam - Caliph Al-Hakim bi-Amr Allah (996-1021) ordered his da'i, Harun bin Mohammed in Yemen, to give decisions in light of "Da'a'im al-Islam" only.