Usul al-Kafi
Book 3: The Book of Excellence of Knowledge

Chapter 15
Transitory-ness of names

217. 3. Imam Ali ar-Reza (p) was asked about the exact nature of name.
The Imam (p): A name is an attribute of the object named.

218. 4. Imam Jafar as-Sadiq (p): The name of God is something other than God Himself. And everything to which the term is applicable except God Himself is a creation (by God, the Creator). Since whatever is expressed by the tongue and whatever is done by the hand is nothing but a creation. And one’s saying God with his tongue or writing ‘God’ with his hands is an extreme limit among all conceivable limits to signify Godhead. But the object represented by a symbol is quite different from the symbol itself. But the symbol can be expressed by sound or by letter and all that can be expressed or defined is something created while the Creator of all things including space, time, abstract concept of how, why, where, and when etc. cannot be expressed or defined to any extent. God was not brought into being so that the state of His being could be known through the works of someone else who brought him into being. And to whatever extreme limit men may rise in His cognition He shall be other than that extreme limit.
Summarizing the above sermon on the Unity of God, the Imam (p) concluded:
One who has comprehended this truth can never go astray. This is the essence of the Unity of God, so by the grace of God, guard it, do not let the shadow of any untruth fall on it. Remain steadfast in it and comprehend it by the will of God. He who pretends or assumes that he knows God through his veils or by forms or by semblance is a polytheist. Because His veil, form or semblance are different from Himself. Verily He is the One, the Unique. So how can a person bear witness to the Unity of God and to His being unique if he thinks that he has known God through nothing other than God? Verily only he has known God who has known God through God himself. He who has not known God through God Himself has not known Him at all. What he has known is something other than all the things when nothing existed. He is called by His names but He is other than His names and His names are other than what He is.