Is the twelfth of Rabi' al-Awwal the day of the Prophet's—peace and blessings be upon him—birth or the day of his death?

The birth date of the Prophet, peace and blessings be upon him, is a matter of disagreement among scholars. Some say it was on the twelfth of Rabi' al-Awwal, others say the second, some the eighth, and yet others the ninth of the same month. As for the day of his passing, peace and blessings be upon him, the majority opinion is that it was on the twelfth of Rabi' al-Awwal, though some say the eleventh of Ramadan (definition).