Muharram is the first month of the Islamic (Hijri) calendar and one of its four sacred months, in which warfare was traditionally forbidden, its very name derives from the sense of that which is forbidden or inviolable. Its first day marks the Islamic New Year, and its tenth, the Day of Ashura, is widely observed: Sunni Muslims often keep it as a voluntary fast, while for Shia Muslims it is a solemn day of mourning commemorating the martyrdom of Husayn, grandson of the Prophet, at Karbala. The Islamic calendar is purely lunar, its twelve months following the phases of the moon and its year of about 354 days making no adjustment to the solar seasons, so the months move steadily earlier through the solar year. These are the observances of the Islamic calendar tradition, in which Muharram opens the year on a sacred and, for many, a mournful note.
Muharram's sanctity, like that of the other three sacred months, predates Islam; pre-Islamic Arabian tribes already observed a truce during Muharram, Rajab, Dhu al-Qadah and Dhu al-Hijjah, and the Quran (9:36) affirms rather than introduces this older custom of four forbidden-to-fight months out of the twelve. The Day of Ashura, the tenth, is also linked in some hadith to a fast the Prophet Muhammad is reported to have observed on learning that the Jewish community of Medina fasted on that date to commemorate the Exodus, after which he is recorded as having encouraged Muslims to fast it as well, later distinguished in significance from the Ramadan fast the Quran would establish as separately obligatory. For Shia Muslims, Ashura's mourning for Husayn at Karbala in 680 CE is marked with processions and, among some communities, ritual self-flagellation, practices not universally observed or endorsed across the wider Shia world.