What is the ruling if sleep overwhelms a Muslim before Fajr prayer, and he expects not to wake up for it, or if he misses the prayer and makes it up after waking up, doing so intentionally to avoid being reprimanded?

Whoever misses a prayer due to sleep or forgetfulness is not sinful, and must make it up immediately upon waking or remembering. This is the view of the majority of jurists. The Shafi'is, however, hold that making up the prayer can be done at leisure for one who missed it with an excuse. As for one who intentionally delays it, the correct view among the Shafi'is is that making it up immediately is obligatory.

Regarding sleeping before the prayer time enters, there is no harm in it, even if one strongly suspects they will not wake up. However, after the time has entered, it is not permissible to sleep unless one knows they will wake up before the time expires, or they assign someone to wake them. One should also take measures to wake up, such as setting an alarm.