From the twelve lunar months of the Islamic calendar there are four sacred, concerning them Allah says:
Verily, the number of months with Allah is twelve months (in a year), so it was ordained by Allah on the Day when He created the heavens and the earth; of them, four are sacred. That is the right religion, so wrong not yourselves therein. (At-Tawbah 9:36)
Four Months Are Sacred
The Prophet (peace and blessings be upon him) also said about them:
“The division of time has turned to its original form which was current when Allah created the Heavens and the Earth. The year is of twelve months, out of which four months are sacred. Three are in succession: Dhul-Qi`dah, Dhul-Hijjah, and Muharram, and (the fourth is) Rajab of (the tribe of) Mudar which comes between Jumada Thani and Sha`ban.” (Al-Bukhari)
So what characterizes these four months, and what should we do in them?
Sheikh Muhammad Salah answers in this video…Soucre Link