Tafsir of Al-`Ankabut 29:21

يعذب من يشاء ويرحم من يشاء

He punishes whom He wills, and shows mercy to whom He wills; He is the Ruler Who is in control, Who does as He wishes and judges as He wants, and there is none who can put back His judgement. None can question Him about what He does; rather it is they who will be questioned, for His is the power to create and to command, and whatever He decides is fair and just, for He is the sovereign who cannot be unjust in the slightest. According to a Hadith recorded by the Sunan compilers:

إن الله لو عذب أهل سماواته وأهل أرضه لعذبهم وهو غير ظالم لهم

If Allah willed to punish the dwellers of His heavens and His earth, He would do so, while He would not be unjust to them. Allah says:

يعذب من يشاء ويرحم من يشاء وإليه تقلبون

He punishes whom He wills, and shows mercy to whom He wills; and to Him you will be returned. You will return to Him on the Day of Resurrection