Probably related to some forms of Mutazilite theology. Also people like ibn Sina and al Farabi perhaps. I don't really know much about the topic though so might be wrong.
There were Muslim philosophers influenced by neoplatonism though as there were in Judaism expressed by people such as Maimonides and Aquinas and Pseudo Dionysus for Christianity
Ibn Sina (I think) denied that God could be described as being truly singular as this put a finite limitation on God for example.
There was certainly an apophatic/negative theological strain in Islam in the Medieval period (as there was in Judaism and Christianity).
I think that this kind of understanding of the unity of God has also developed natively within Islam.
Although no doubt, philosophies influenced each other.