Prophet Muhammad 's mosque, Medina
The inside of mosque
(photos are taken at summer 2008)
In the Islamic calendar, the 12Th day of Rabi-al-Awwal marks the birthday of the Prophet Muhammad (peace be upon him).
There is a difference of opinion about whether the Milad An-Nabi (Prohet Mohammad's Birthday) should be a time of celebration. There is evidence that the Prophet, his Companions, and the early followers after them did not celebrate or otherwise observe his birthday. On the contrary, Muhammad was careful to warn his people not to imitate other faiths, whose followers elevated their prophets and added to the religion what was not in the original teachings.
Those who disagree claim that although not practiced in the early years of Islam, the remembrance of the Prophet's birthday is a "good innovation." They see it as a time to read the Qur'an, and remember the life, teachings, and example of the Prophet Muhammad.
Reference of the text :about.com