Is obedience to one's parents obligatory when they ask one to sleep at night, if the questioner stays up to pray Fajr and then sleeps, justifying this by stating that he would not wake up for the prayer if he were to sleep early?

Obedience to parents is obligatory in matters that benefit them and do not harm the child. However, in matters that do not benefit them or cause harm to the child, obedience is not obligatory. If staying up late leads to the parents' welfare being neglected due to sleeping for long hours during the day, then obedience is obligatory. But if the child attends to their needs and serves them without shortcomings, then obedience is not obligatory regarding not staying up late. If performing the Fajr prayer is difficult except by staying up late, then there is no harm in staying up late for a matter that benefits you, such as praying Fajr on time, while placating the parents and explaining the reason. One must be keen on performing prayers on time, especially Fajr, while seeking alternatives to staying up late, such as an alarm clock or asking for help to wake up, in order to combine the benefit of prayer, pleasing the parents, and the well-being of the body.