There are some similarities between the old Muhammedan Calendar and Umar's Hijri Calendar visible even today despite some position changes. For example the month names: Sivan/Ṣafar, Elul/alŪlā, Cheshvan/Shaʿbān, and Shevat/Shawwāl. Also, the major Hajj of the year is in the originally spring month of Dhū al-Ḥijja exactly like Passover in Aviv (spring). This is followed by the fasting of Iyyar/Muḥarram commemorating the deliverance from Egypt. Moreover, the 7th month is still sacred in both. Finally, Ramadan corresponded corresponds to the old Julian Calendar's month of December of course.
