ما هو شرح التقويم الهجري والميلادي، وتسلسل الأحداث والعصور في حياة المسلمين؟

The Hijri calendar was adopted by Umar ibn al-Khattab, may Allah be pleased with him, after consulting with the Companions. In contrast, the Gregorian calendar was adopted by a Christian monk, starting from the year he speculated Jesus, peace be upon him, was born. There is no proof for this date; in fact, his birth could have been in the summer. It is advisable to consult books of Islamic history and biographies for the sequence of events, such as Al-Bidayah wan-Nihayah by Ibn Kathir. The Hijri calendar must be adopted because it is the one relied upon for timing acts of worship.