Al-Abbas ibn al-Ma'mun
... that Arab prince Al-Abbas ibn al-Ma'mun refused to take the throne even though he was the only son of the previous caliph and had the support of the army?
... that <a href="./Abbasid_Caliphate" id="mwErM" rel="mw:WikiLink" title="Abbasid Caliphate">Arab prince</a> <b id="mwErQ"><a href="./Al-Abbas_ibn_al-Ma'mun" id="mwErU" rel="mw:WikiLink" title="Al-Abbas ibn al-Ma'mun">Al-Abbas ibn al-Ma'mun</a></b> refused to take the throne even though he was the only son of the previous <a class="mw-redirect" href="./Caliph" id="mwErY" rel="mw:WikiLink" title="Caliph">caliph</a> and had the support of the army?