Question: We know that ‘Ibaadah (worship) is determined by the Will of Allaah; were it not for this Will, no one would have performed `Ibaadah. Sin is determined by the Will of Allaah as well; but for this Will, no one would have sinned. Although Allaah is never unjust, why does He reward those who worship Him, although they were destined to do so? Why does He torture sinners, although they were destined to do so?
Answer: The principle in this is that Allaah (Glorified and Exalted be He) is the Disposer of the affairs of His Creatures; He cannot be questioned as to what He does, while they will be questioned… read more here.