Is it been told in Quran that Muslims have to fast during Ramadhan, while hijrah year was only found by Omer Khatab (ra)?

As salaamu alaykum wa rahmatullahi wa barakatuhu%0D%0A%0D%0ADear respected sister in Islam,%0D%0A%0D%0AThe twelve months of the lunar calendar were in existence before Islam. There were some sacred months in which tribal wars were prohibited. The Arabs use to change those months to suit their purposes. Almighty Allah Ta'ala upheld the twelve lunar months and condemned the practice of changing the months (sura Tauba verse 36). When Rasulallah (Sallallahu-Alaihi-Wasallam) performed Haj, he announced that the day, month had returned to the original order and sequence. The Quran states the obligation of fasting in sura Baqarah verse 183. Rasulallah, Sallallahu-Alaihi-Wasallam fasted in the month of Ramadan. The Islamic calendar commences with the year of hijrah and that was clear. There was no need to found the hijrah year. However, since Rasulallah Sallallahu-Alaihi-Wasallam came to Medinah Munawwarah in Rabiul-Awwal, there was a discussion whether the year should commence from Rabiul-Awwal or Muharram. Hadhrat Umar (Radhiallahu Anhu) approved of commencing the year from Muharram.%0D%0A%0D%0AAnd Allah Ta'ala knows best%0D%0A%0D%0AMufti E.Desai