Muslims believe in the lunar calendar, which is about twelve months long. The first month, Muharram, is dedicated to mourning the death of the Prophet Muhammad's grandson, Hasan. The tenth month, Shaaban, commemorates the battle of Badr. The following month, Ramadan, is the most important month in the Muslim calendar. It is during this month that Muslims fast from sunrise to sunset. Muslims also pray during Ramadan, and give charity to the poor. The final month, Shawwal, is devoted to fasting from sunrise to sunset again, and also to making pilgrimages to Mecca.