Is a car accident caused by a son due to speeding considered to be "qadaa' wa qadar" (divine decree and destiny)?

Everything that occurs in the universe, great or small, is by the decree, preordainment, knowledge, and will of Allah, as stated in the Almighty's words: "Indeed, We created all things with a [decreed] measure" and "and He created each thing and determined it with [precise] determination." The fact that a person is the cause of an action does not remove that action from Allah's decree. What happened to your son is from Allah's divine decree and preordainment. The Prophet, peace and blessings be upon him, urged taking precautions and adopting means. If the desired results are not achieved, it means that Allah did not decree them, for he said: "Be keen on what benefits you, seek help from Allah, and do not lose heart. If anything befalls you, do not say, 'If only I had done such and such, it would have been such and such,' but rather say, 'Allah has decreed, and what He wills, He does.'"