Bismillahir Rahmanir Rahim
Assalamu alaikum warahmatullahi wabarakatuhu
They ask you,[O Muhammad], about the New Moons. Say, "They are measurements of time for the people and for hajj [Pilgrimage]." (Al-Quran 2:189)
Allah says: Indeed, the number of months with Allah is twelve [lunar] months in the register of Allah [from] the day He created the heavens and the earth; of these, four are sacred. That is the correct religion, so do not wrong yourselves during the sacred months. (Al-Quran 9:36)
The Prophet (peace and blessings of Allaah be upon him) said:“The best fasting after the month of Ramadaan is fasting in the month of Muharram.” (Narrated by Muslim)
Prophet (pbuh) said:...."fasting on the day of Aashura (the 10th of Muharram) gives forgiveness of one past year"
The Islamic calendar, just like the Gregorian one has 12 months. Islamic Month are: