Before spawning, the Buyids did a mighty fine job of smashing the Abbasids which meant that the Spiral Minaret had not yet been built.
So I chose not to initially spread Shia Islam in my capital, which allowed Sunni Islam to spread there and first up after a Blacksmith was the Spiral Minaret. Shortly thereafter Hinduism was also spread to my capital by an Indian missionary and Rani Kav was the next build in my capital.
I captured Multan early and spawned 5 Great Priests there, while spreading Shia to most of the Seljuk, Ghaznavid and Khwarezmid cities. I then converted each of these civs to Shia Islam by bribing them with techs and suddenly there were 12 settled Great Priests in Shia-controlled cities.
Just as I was considering taking Al-Kufah from the Rebels, the Abbasids respawned and I had to bide my time building up more troops for a push on Al-Kufah. In the meantime my fleet took a raiding party to capture Mecca (Rebel) and Medinah (Fatimid). Mecca had one Islamic Relic too. Fatimids were doing great, so I sued for peace after taking Medinah and they stayed more than stable enough to prevent the Mamluks from spawning.
Once I had enough troops ready, and just before the Mongol invasions entered Iraq, I declared war on the Abbasids and beelined for Al-Kufah. I then holed up inside the Shia Holy City whilst the Mongols began to dismantle the Abbasids. After a brief pause, my troops ventured north from Al-Kufah and took Baghdad from the Abbasids, which conveniently had three Islamic relics inside!