Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah (PBUH) said, "The best month for observing Saum (fasting) next after Ramadan is the month of Allah, the Muharram; and the best Salat (prayer) next after the prescribed Salat is Salat at night (Tahajjud prayers)."[Muslim].
Reference of the month to Allah is a sign of its distinction and auspiciousness like Baitullah, Naqatullah etc. Muharram is one of the sacred months and it is this month with which the Islamic year starts. The other three sacred months are Rajab, Dhul-Qa`dah, and Dhul-Hijjah. The Hadith points out that fasting in the month of Muharram is better than any other month of the year after Ramadan.