In what century (CE) was Ramadan first observed as a month of fasting, introspection and virtue?

Question

What is the 9th month of the Islamic calendar, the month of fasting, in which Muslims refrain from eating, drinking, smoking, and so on from dawn to sunset?

Answer 1

7th
Ramadan is the month which Islam commemorates as the one in which the Quran was first revealed to Muhammad.