What was the first day of the first Ramadan that the Prophet, may God's prayers and peace be upon him, fasted?

The first day the Prophet, may God's prayers and peace be upon him, fasted in Ramadan was a Wednesday, as the fasting of Ramadan was mandated in the second year of the Hijra. The Prophet fasted nine Ramadans. The Battle of Badr occurred on the seventeenth of Ramadan, a Friday, which indicates that the first Ramadan began on a Wednesday. Knowing this specific day holds no particular significance and no ruling is based upon it.