Hijra dates are being observed in different Gregorian Calendar Days in different parts of the World. But the Universal time difference is only 24 Hours for a day. All other Calendars show Day & Date as same all over the World, except for the time difference of24 Hours. Then How come this difference in Hijra Dates alone ?. Some scholars argue that the visibility of Crescent Moon is the basis for starting new Hijra Month, some others argue that the Day succeeding to Conjunction Date (New Moon) is the start of a new Hijra Month. Does it all mean that, there is no proper method in ISLAM to compile Hijra Date? What is Quranic Notion on it?. Also make it clear Whether Quran refers anything about Solar Calendar ?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.

First of all, the start of the lunar month is not calculated based on the Gregorian Calendar as you suggested but on the sighting of the new moon (crescent). Allaah The Exalted says (what means): {They ask you, (O Muhammad), about the new moons. Say, "They are measurements of time for the people and for Hajj".} [Quran 2:189]

The Prophet said: “The year is twelve months, four of which are sacred. Three of them are in succession – Thul-Qiʻdah, Thul-Hijjah and Al-Muharram, and (the fourth is) Rajab of (the tribe of) Mudhar, which comes between Jumaada and Shaʻbaan.” [Al-Bukhari]

The Prophet also said about the month of Ramadan: “Observe fasting with its sighting and break it with its sighting.” [Al-Bukhari and Muslim] This adequately underlines the method of determining the beginning and end of the lunar month.

As for the unification of the Islamic Hijri calendar all over the world, nothing in the Quran or the Sunnah explicitly states that the beginnings and ends of the lunar months should be unified all over the world. Rather, Muslims should determine the beginning and end of the lunar months by the sighting of the moon. Whenever Muslims see the moon of Ramadan in any part of the world, they must observe fasting, and those who do not see it should not observe fasting until it is seen. We have highlighted in Fataawa 81595, 92309 and 138991 that the differences in the sighting of the moon has been common and acceptable throughout the history of Islam and that the matter is open for Ijtihaad (personal reasoning by competent scholars). The differing on this matter is tolerable within the Muslim Ummah and each has evidence to support his view.

The fact that the beginnings and ends of the lunar months depend on the sighting of the moon does not mean that the sun has nothing to do with calculating time. Rather, both the sun and the moon are both relied on in calculating time. Allaah The Exalted says (what means): {(He is) the cleaver of daybreak and has made the night for rest and the sun and moon for calculation. That is the determination of the Exalted in Might, the Knowing.} [Quran 6:96] Al-Baghawi commented, “It means that the positioning of the sun and the moon is relied on in calculating time. If it were not for the day and night and sun and moon, we would not be able to calculate time.”

Allaah also says (what means): {It is He who made the sun a shining light and the moon a derived light and determined for it phases - that you may know the number of years and account (of time).} [Quran 10:5]

At-Taahir ibn ‘Aashoor said, ”The verse refers to calculating the beginning and end of months based on the positioning of the moon because the pronoun in the verse refers to the moon. The seasons, on the other hand, are determined by the positioning of the sun.”

Without doubt, determining the prayer times depends on the positioning of the sun and not the moon. Thuhr prayer is due when the sun is at its zenith in the middle of the sky, ʻAsr when the shadow of everything is equal in length to the object itself, Maghrib prayer at sunset, and so on. However, the beginning and end of the lunar months are determined by the sighting of the crescent and the number of days and the duration and length of days and nights depend on the sunrise and sunset.

As for the question about whether the Quran refers to the solar (Gregorian) Calendar, some Tafseer scholars have stated that the reference to the three hundred and nine years mentioned in the verse [18:25] actually means three hundred plus nine years in lunar years, which is three hundred years in solar years. Allaah The Exalted says (what means): {And they remained in their cave for three hundred years and exceeded by nine.} [Quran 18:25] Ibn Katheer commented, “The length of time was three hundred plus nine years in lunar years, which is three hundred years in solar years.”

Allaah Knows best.