If it is just a "thought" or a "self-talk", then the servant will not be held accountable for it as long as he does not speak or act upon it.
The Prophet (ﷺ) said, "Allah has forgiven my followers (Ummah) the evil thoughts that occur to their minds, as long as such thoughts are not put into action or uttered."
" إِنَّ ...
Wa 3laykum As Salaam,
I hope you are doing well. Waswasa (whispering) are thoughts that arise from an external source (i.e shayateen (evil jinn/djinn), etc.). We see from the below sources that the whisperings are not positive thoughts but negative thoughts / ill feelings towards yourself or others. These thoughts can lead people to doubt. The best thing is ...
That because maybe you don’t really know Allah, I suggest you to read this ayat that god introduced himself by himself
And by understandig what the meaning of the 99 names of allah and read more Quran especially when allah talk about himself you will know who is Allah.