Whilst authorities are divided on the Prophet's
birthday, there seems a general consensus about his death day. For the former,
the 9th or 12th of Rabī al-awwal are the probable dates, while for the latter
the date put forward is the 12th of Rabī al-awwal.
We are not required to celebrate this day by our religion.
In fact, making the celebration a religious requirement is an innovation (bid`at).