What is the ruling on saying "in sha' Allah" (God willing) after a supplication (du'a), such as "May Allah reward you with good, in sha' Allah" or "May God grant you success, in sha' Allah," given the prohibition against saying "if You will" in a du'a?

The prohibition against saying, "O Allah, forgive me if You will," in supplication is due to its being reprehensible, and it encompasses all types of supplication, because nothing that Allah grants can ever be impossible for Him. Supplication must be assertive, showing intense desire and diligence, and not despairing of Allah's mercy. For Allah Almighty answered the supplication of Iblis despite his evil.