Most Muslim holidays follow the Islamic calendar, which is different from the Gregorian calendar. The most important Islamic tradition is the Hajj. The Hajj is the pilgrimage to Mecca. Every Muslim is supposed to make the pilgrimage in his or her lifetime, if they are able to.
The main Islamic holidays are: Ramadan, Eid al-Fitr, and Eid al-Adha. Additional holidays are Mulid al-Nabi, Birthday of the Prophet, Layla al Bara’ah, Night of Forgiveness, Laylat al-Miraj, Night of the Ascension, Laylat al-Qadr, Night of Power, and Ashura.
Gulevich, Tanya. Understanding Islam and Muslim Traditions: An Introduction to the Religious Practices, Celebrations, Festivals, Observances, Beliefs, Folklore, Customs, and Calendar System of the World’s Muslim Communities, including an Overview of Islamic History and Geography. Detroit, MI: Omnigraphics, 2004. Print.
To read Understanding Islam and Muslim Traditions, please see the attached document.