Is it permissible to pray Fajr before its prescribed time to avoid missing it due to going to bed early for work?

It is not permissible to pray before the time for it has begun. Whoever does so must repeat the prayer, because the beginning of the prayer's time is a condition for its validity. If a Muslim sleeps, he must take measures to wake up for the prayer. If he is overcome by sleep and does not wake up until after the time for the prayer has expired, there is no sin upon him, and he must pray immediately upon waking up.