The Karluk mercenaries don't defect to the Muslims in the Battle of Talas, while the battle is still a loss for the Tang Dynasty, it does present an interesting PoD.
Whether it is because of brutal reprisals facilitated on the Turkic mercenaries after the battle or just the pettiness of a sore loser, it causes a chain of events that either considerably slows down the adoption of Islam by the Turks or just shuts down even a shred of possibility of it being the case. This is course means the future of the middle east becomes unrecognizable, though I can't say the exact details.