Mukhtasar Bukhari

Narrated by Sayyiduna Abu Bakrah (may Allah be pleased with him) from the Prophet Muhammad (peace and blessings of Allah be upon him) that he said: "Time has come back to its original state as it was on the day Allah created the heavens and the earth. The year is twelve months, of which four are sacred; three are consecutive: Dhu al-Qa'dah, Dhu al-Hijjah, Muharram, and (the fourth) Rajab of Mudar (the tribe of Mudar used to venerate it greatly), which is between Jumada al-Thani and Sha'ban."