Should Muslims follow the Hijri calendar?

“It is permissible to fast on the last and first day of the Islamic year. The Hadith explains that besides five days of the year, fasting throughout the year is permissible. However, we have not come across any of the authentic Ahaadith that fasting on the last and first day of the Islamic year is a sunnah practice.”

“For the past 1,400 years, it’s the Ijma (consensus) of all four Madhahib that the birth of a new moon according to astronomical calculation is not the determining factor for commencement of a new Islamic month, but the actual sighting of the crescent is the determining factor.”

“There are many divine laws based on the lunar calendar. For example, Ramadan is in the ninth month of the lunar calendar and Dhul Hijjah is in the twelfth month of the lunar calendar. Allah Ta'ala also indicates towards the Islamic Calendar in the Quran:”

“Rasulullah Salallahu Alaihi Wasallam is reported to have said, “Whoever licks honey three mornings every month, will not suffer a major calamity.” [Ibn Majah – Hadith no. 3450]”