What is the ruling on saying "In sha' Allah" (God willing) in matters of the Hereafter, such as "In sha' Allah, he will be punished," or "In sha' Allah, I will exact retribution from him in the Hereafter"?

Making an exception with "in sha' Allah" (God willing) in matters of future events, whether probable or certain, is permissible. In the case of certain events, it is considered for affirmation, not for suspension. Texts have indicated the permissibility of this exception even in matters of the Hereafter that are certain to occur, and it is interpreted as seeking blessings and affirming, not as expressing doubt. Examples include the Almighty's saying: {You will surely enter the Sacred Mosque, if Allah wills, in security} [Quran 48:27], and the Prophet, peace and blessings be upon him, said: "No one from the Companions of the Tree shall enter Hellfire, if Allah wills," and "I want, if Allah wills, to reserve my supplication as intercession for my Ummah on the Day of Resurrection."