Will Allah punish us for abandoning the Sunnah of the Prophet (peace and blessings be upon him), such as shaving the beard or not praying the two rak'ahs before Fajr (Sunnat al-Fajr)?

"Sunnah" is used to refer to a way or guidance, and also to that which is recommended (mustahabb), for which one is rewarded for doing it but not punished for leaving it. There is no punishment for abandoning that which is recommended. As for "Sunnah" in the sense of a way, it is divided into obligations (wajibāt) and supererogatory acts (nawāfil). The Sunnah of Fajr and Witr prayers are emphasized Sunnahs. Growing the beard is among the obligations, not recommended Sunnahs, and one who abandons obligations is punished. "Sunnah" is also used in contrast to innovation (bid'ah), and following it is obligatory.