Using the Gregorian calendar in a company's dealings

Q: Your Eminence, as you know, there are daily business relations with different parts of the world. Our company is involved in this activity one way or another. This kind of fast connection with other companies in the globe requires (Part No. 26; Page No. 398) coordinating the daily fiscal calendar, while our internal policy permits the use of the Hijri Lunar calendar or the Christian calendar for the companies during the fiscal year for each company individually. I would not be wrong if I said that the majority of the large financial organizations in our country are now adopting the Christian calendar. Our commercial relations with such organizations prefer daily business correspondence in this way, but we work according to the Hijri calendar. We would like to know Your Eminence's opinion regarding using the Christian calendar for the activities of the company, and calculating the fiscal year of the company in accordance with the Christian calendar? Is this Haram (prohibited) or Halal (lawful)?Please give us the legal opinion in this regard, for you are the Imam of sincere and truthful Muslim jurists. May Allah increase you in piety and bless you. Your service to Islam and Muslims is known to one and all.

A: You should adhere to the Hijri calendar as has always been adopted by Muslims since the era of Al-Faruq (Umar ibn Al-Khattab) (may Allah be pleased with him) until our present time, because it is an honor for the Islamic Ummah (nation) to have an Islamic calendar of its own.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.