Is it permissible to hasten the performance of the Fajr prayer so as to perform it before sunrise, and to postpone the Sunnah (of Fajr) until after sunrise?

It is permissible to hasten the prayer when there is a fear of the time expiring, provided that tranquility (طمأنينة) is not violated. This means that the limbs must settle in the posture of each pillar. If hurrying disrupts tranquility, the prayer becomes invalid and must be repeated. According to some scholars, whoever catches the opening Takbir (Takbirat al-Ihram) or less than a full Raka'ah before the time expires is considered to have performed the prayer on time. One must take measures to wake up; otherwise, the worshipper incurs sin.