The following are excerptions from the long narration and the well-known session in which Imam Rida (AS) overcame all the theologians of the various sects opposing Islam whom were gathered by Al-Ma'mun for disputation.
Imran Al-Sabi said to Imam Rida (AS): Do we declare the oneness of Allah by reality or by description?
Imam Rida (AS) answered: Certainly, Allah the light, the Initiator of this cosmos, and the Foremost is One without any associate or any accompanying thing. He is Unique without a second. He is neither realized nor unknown.
He is neither decisive nor allegorical. He is neither mentioned nor forgotten. He is not a thing that familiar name can fit Him. The Initiator has been Self-existent and light that is dispending with everything. He did not exist in a definite time and will not last for a definite time. He has not existed in anything. No sayer can invent a statement describing Him even if he thinks of light, example, ghost, or shadow.
All that was before the creation and in the situation where there was nothing but Him. The same situation is in this position. There are only imaginary attributes and a translation of a picture in the mind purposed for making others understand. Did you understand, Imran?
Imran answered affirmatively.
The Holy Imam (AS) then went on: You should know that imagination, innovation, volition, and will have the same meaning although they are three expressions. The foremost of His imagination, volition, and will is the letters that He made the origin of everything and the answer for every problem. He has not decided in His imagination a meaning, other than the finite and existent, because nothing was before or with Him.
Imagination, however, preceded the letters; therefore, they became new by means of the imagination. The imagination was existent when there was no trend before Allah. The imagination of Allah is something different from Him. On that account, the action of a thing is something different from it, the edge of a thing is something different from it, the feature of a thing is something different from the thing that is described with that feature, and the border of a thing is something different from the thing is related to that border. Letters are broken up and scattered things that have no single indication. When they are combined in a definite arrangement, they will refer to other things like names and features.
You should know also that there is no feature to the indescribable, no name to the meaningless, and no edge to the edgeless. All the names and features refer to perfection and existence, but do not refer to encirclement, like their referring to the terms such as squares, circles, and triangles, because Allah can be recognized through names and attributes and not through terms.
Allah is not subject to any terms; therefore, the creatures cannot recognize Him in the same way they recognize themselves. If His attributes and names do not refer to Him, then the creatures are worshipping His names and attributes, not their meanings. If this is true, the worshipped god will be someone other than Allah, since His attributes refer to something other than Him.
Imran asked: Is imagination a created being or not?
Imam Rida (AS) answered: Imagination is a created inactive being that cannot be realized by inactivity. It is a created being just because it is originated by Allah. Because it is called a thing. it becomes a created being. There are only two things - Allah and His creatures. A created being can be inactive, moving, variable, static, familiar, or obscure. Any being that acquires a name is created.