It is narrated from Hazrat Sha’bi that Hazrat Abu Musa wrote to Hazrat Umar (may Allah be pleased with him) that letters from you reach us, but we do not know their date, so please fix a date for us. Hazrat Umar (may Allah be pleased with him) consulted the noble Companions (may Allah be pleased with them). Some Companions suggested that the date should be fixed from the Prophethood of the Messenger صلی اللہ علیہ وسلم , and some other Companions suggested that the date should be fixed from the passing of the Messenger صلی اللہ علیہ وسلم . Hazrat Umar (may Allah be pleased with him) said: I will fix the date from the Hijrah of the Messenger صلی اللہ علیہ وسلم , because the Hijrah of the Messenger صلی اللہ علیہ وسلم is what distinguished between truth and falsehood. Thus, he fixed the date from the Hijrah.