First of all the day of 'Ashura' was the first ordered fast in Islam and it was ordered on the first 'Ashura' after our Prophet (pbuh) moved to Medina, as the hijra was in Rabi' al-Awwal according most scholars, this 'Ashura' should have been in the year 2 after hijra, the same year most scholars assume that fasting Ramadan was ordered. And by the order of ...
Both decisions, ie when to start the Islamic calendar and what its first month should be, were consulted upon and decided by the Sahabah [may Allah (ﷻ) be pleased with them], who agreed that it was the best to start the calendar based on the Hijrah and to start the calendar with Muharram as the first month.
Why did they choose Muharram over Rabbi Al Awwal? ...
Assalaamu alaikum warehmatullahi wabarakatuhu
In the name of Allah the most Gracious the most Merciful
Volume 3, Book 31, Number 222 :
Narrated by Ibn 'Abbas
The Prophet came to Medina and saw the Jews fasting on the day of Ashura. He asked them about that. They replied, "This is a good day, the day on which Allah rescued Bani Israel from ...
In regard to the importance of Taasuaa (تاسوعا) as the ninth day of Moharam, it is quoted that Imam Jafar-a-Sadiq (peace be upon him) said:
عن الصادق (عليه السلام) قال: تاسوعاء يوم حوصر فيه الحسين (عليه السلام)
وأصحابه بكربَلاءِ واجتمع عليه خيل أهل الشام وأناخوا عليه، وفرح ابن
مرجانة وعمر بن سعد بتوافر الخيل وكثرتها واستضعفوا فيه الحسين (عليه