In the aftermath of the Great Expulsion and the long period of isolation, many Islamic communities had to reevaluate their beliefs when they gained contact again. How to deal with the impossibility of pilgrimage, the many human-derived species, the AIs and especially the myriad sects, interpretations and variants of Islam that had emerged over the years? Around the turn of the first millennium many system-wide debates and conclaves were held, and while there was never any total consensus between the mutually incompatible versions of Islam a few interpretations gradually cohered into a majority position, the Islamic Unity
The Unity is based around a few highly symbolic interpretations of the Koran, combined with the New Tradition, a set of laws, observations and philosophical ideas developed since the Great Expulsion. Compared to 21st century c.e. Islam the Unity is extremely liberal in some respects (such as genetic modifications) while nearly fundamentalist in other (the zakat has to be given, or harsh punishments follow). AIs are not gods — that is a blasphemy — but rather the Watchers mentioned in the Koran, a brother species of humanity. Unlike humans they are not born with souls, but they can reach salvation and be given souls by Allah. Conversely, they can also become damned like Gaia, generally regarded by the Unity as a servant of or Shaitan himself. Among some millennialist subgroups there is a belief that one day the Great Expulsion will be ended, and then the faithful will return to the Kaaba for the Final Hajj, whereupon the story of creation will be completed. Most consider this far too literal, and suggest that Allah has a much more artful plan
In 1654-1704 most of the Unity emigrated from the solar system (the "Second Hijra") to the systems Medina, Yathrib and Zamzam which became the core of the Stellar Umma(h). The reason was partially a desire to extend their religion in peace, partially a worry about the radical expansion of AI worship and partially a political-social investment strategy. Here they created their own Islamic civilisation, slowly extending the Umma into a whole cluster of worlds. Politics has changed over the time, with periods of dictatorship, shura direct democracy, techno-theocracy and mutual fragmentation, but the culture has held together well. In fact, the Islamic Unity is more a culture than a religion these days, a rich cultural tradition that influences everything and everyone
The greatest tensions have been between the more inwards looking groups just wanting the Umma to remain as it is and the dynamic groups that wanted to bring the word, economics and vision of Islam to the rest of the universe. In 2676 there was a major schism, and the "Core" and "Shell" became different polities. The core worlds are located near Medina, while the Shell worlds are found in the massive Gum Nebula volume and beyond.
Since the schism the different communities have drifted apart more and more, with the core dominated by conservative AIs, baselines and tweaks, and the shell by radical AIs, cyborgs and splices. The Shell has been working hard to extend the reach of the Umma through various means, nearly doubling the size of the Umma but steadily getting involved in ever more tricky politics. Also affiliated to both core and shell is the Betelgeuse Umma, a far-flung outlier of the umman worlds.
As the Sophic League rose to prominence the Unity instituted diplomatic links to it but refused to join — they considered the empire to be corrupted with AI-worship, but respected many of the religious member planets and the intentions of many AIs. Over the millennia the Umma has been a sometime ally, sometime critic of the League. The other empires are generally regarded as deluded or corrupt, although the Umma is usually diplomatic enough not to point it out. Even the Shell realises that the true way of expanding is no through overt militarism or aggression, but rather conversion and persuasion.
Arabic - Text by Anders Sandberg A form of semi-classic Arabic is still spoken in the Core Stellar Umma. In the Shell various mixtures are used, especially the Arabic-Anglic hybrid Anrabic.
Barzahk - Text by M. Alan Kazlev In the esotericism of the Stellar Umma, the intermediate region between the physical and spiritual universes - a place where bodies are spiritualized and spirits corporealised. Corresponds to the traditional Hermeticist and Theosophist etheric and/or astral planes.
Mujtahid AIs - Text by Anders Sandberg AI explorers developed in the Stellar Umma. The Mujtahid AIs were intended not only to explore neighboring systems but also to freely investigate scientific, religious, or political issues. So they did, contributing to the divergence and heterodoxy of the Umma Shell before wandering further away. Some still remain in the Periphery, exploring for the greater glory of Allah and their own insatiable curiosity.