Hold it.

Who said that there is any such thing as "thinking"?

Is "thinking" a verb?

Does "thinking" require a 'thinker'?

All of this is a violation of Occam's Razor: "Do not unnecessarily postulate multiplicity"; or "the simplest answer is the best answer".

Thus, there is neither "thinking" nor a 'thinker'.

There is only thought: the thought of the 'thinker' and the thought that there is a verb "to think".

Can any of this be proven?

Not at all.

It is prior to thought.

It can only be observed as being an accurate description.

Michael