What is the effect of du’a upon the destiny?
Dua can change the destiny. Still, this change is written in the Preserved Tablet (اللوح المحفوظ Al-Lauhul-Mahfud). There is a saying of Prophet Muhammad, peace be upon him, stating that supplication and destiny sort of struggle with each other and whoever wins, this will happen. So Allah made the supplication as a reason or a means to push back an unpleasant decree.