Vedic Roots of Ramadan

The difference between pre-Islamic Ramadan and Islamic Ramadan is, pre-Islamic Ramadan was practiced by a Pagan tribe in Arabia, and Islamic Ramadan is practiced by Muslims all over the world.

During Ramadan, Pagan Arabs used to abstain from food, water, sexual contact etc. Muslims practice the same Pagan Ramadan rituals.

It is a well-known fact that Islam adapted the Pagan practice of fasting. There is a Hadith in Sahih Bukhari that mentions the ritual.

Bukhari 5:58:172 – Narrated Aisha: ‘Ashura was a day on which the tribe of Quraish used to fast in the pre-lslamic period of ignorance. The Prophet also used to fast on this day. So when he migrated to Medina, he fasted on it and ordered (the Muslims) to fast on it. When the fasting of Ramadan was enjoined, it became optional for the people to fast or not to fast on the day of Ashura.’
http://www.usc.edu/org/cmje/religious-texts/hadith/bukhari/058-sbt.php#005.058.172

The fasting for Ashura (10th of Muharram) originated from a Quraish Pagan practice. Ramadan fasting came later from Sabian tradition. Sabians are mentioned in several verses of the Quran [al-Baqarah 2:62], [al-Hajj 22:17] , [al-Maa’idah 5:69] along with Christians and Jewish. Sabians, a non-Muslim Iraqi tribe, believed in monotheism, observed fasting 30 days a year, and prayed 5 times a day.

Pre-Islamic Pagans prayed five times a day facing Mecca. Persian Zoroastrian tribe prayed five times a day too, in the direction of the Sun or fire temple. Before prayers, Zoroastrians cleaned themselves or practiced ablution. Ablution and the prayers for 5 times are not something Islam invented. The Hadith [Sahih Bukhari Book 8, no. 345] tells us that when Muhammad met Allah in heaven, Allah demanded 50 prayers per day. But with the help of Moses, Muhammad bargained with Allah and finally he was successful to reduce 50 prayers per day to 5 prayers per day. Even the Quran (4:28) says, ‘God wishes to lighten your burden, for the human being is created weak’.

Many non-Islamic Pagan rituals are now known as Islamic rituals. Pagan’s crescent moon: the symbol of the moon god, circumambulation, Ihram etc. were taken

More details here :
http://religionresearchinstitute.org/ramadan/roots.htm