The ʿAdliyyah said: It is not permissible for Allah Exalted is He to fail in fulfilling the promise and the threat, because that is a quality of deficiency, and Allah is exalted above every deficiency. He Exalted is He has said: “The word will not be changed with Me, and I am not unjust to the servants.” [Qāf] And He Exalted is He said: “Indeed, Allah does not fail in His promise.” [Āl ʿImrān]
The determinists said: Rather, it is permissible for Allah to fail in that.
The response is that Allah Exalted is He says: “That is the Book in which there is no doubt, a guidance for the righteous.” [al Baqarah] If we were to allow the possibility of Allah failing in the promise and the threat, doubt would enter into the verses we have mentioned, and doubting any part of the verses is disbelief.