Upon what basis is the will in His (the Almighty’s) saying: "He forgives whom He wills and punishes whom He wills"?

The absolute will of Allah is not specified except by a legal proof. Among the most important restrictions is His saying, the Almighty: {Indeed, Allah does not forgive association with Him, but He forgives what is less than that for whom He wills}. So, what is less than polytheism is subject to Allah’s will; He forgives by His grace or punishes by His justice.

Al-Harith al-Muhasibi, al-Qasimi, and Ibn Taymiyyah clarified that this verse indicates that Allah does not forgive polytheists, and that He has the will to forgive what is less than polytheism for whom He wills, and that it is one of the strongest proofs for pardoning those who committed major sins before repentance.

Allah’s will follows His wisdom and knowledge, as indicated by the verse: {And you do not will except that Allah wills. Indeed, Allah is ever Knowing and Wise}. The characteristics of those whom He forgives or punishes are derived from detailed evidence, such as His saying, the Almighty: {Those who disbelieved will have a severe punishment, and those who believed and did righteous deeds will have forgiveness and a great reward}. Allah has clarified the characteristics of the people of Paradise and the characteristics of the people of Hell in multiple verses, and He does not punish believers and forgives those who repent.