an uncompounded, primordial substance [jawhar asli basit] within its own identity, alive throughout all its operational states. However, it does not fall beneath the constraints of speculative, sensory perception, and it cannot be observed or found except when manifested within a body."
And Hamza ibn Shu'bah said in the Book of the Knower's Proof [Kitab Hujjat al-'Arif]: "And I maintain that the souls governing the bodies of living creatures are simple, not composite.
The evidence for this is that physical bodies act as mere instruments for them, joining with them in a union without 1 physical intermixture—just as fire unites with a wick, illuminating through it without intermixing with it. Therefore, just as it is impossible for fire to exist visibly except within a physical body to which it attaches because of its simple, elemental nature, likewise the soul cannot be seen except within a body, and it must possess a body by virtue of existential necessity."