The number of months in the sight of Allah is twelve (in a year), so ordained by Him the day He created the heavens and the earth; of them four are sacred: that is the straight usage. So wrong not yourselves therein, and fight the Pagans all together as they fight you all together. But know that Allah is with those who restrain themselves.
 Verily the transposing (of a prohibited month) is an addition to Unbelief: the Unbelievers are led to wrong thereby: for they make it lawful one year, and forbidden another year, in order to adjust the number of months forbidden by Allah and make such forbidden ones lawful. The evil of their course seems pleasing to them. But Allah
The Islamic calendar is based on the year prophet Muhammad and his fellow Muslims (known as Sahabah, the Companions) emigrated to Madinah in the year 622 C.E. (Christian Era). The emigration took place after thirteen years of persecutions by the disbelievers of Makkah. By the command of Allah, the Prophet left the city with his companion Abu Bakr Siddique (R.A.) and escaped a death threat by the disbelievers. The event marks the beginning of a second phase of the Islamic movement. It is the phase when Madinah became the center of an Islamic state.