Your friend is most likely a new revert to Islam or he is ignorant.

The hadeeth is in Saheeh Muslim where the Prophet salla Allahu alaihi wa sallam said that fasting the Day of Arafat expiates two years.

I want to know the importance of fasting on the first 9 days of dhul hajjah specially on 9th. My friend is arguing with me that there is no where mention in the quran to fast on 9th of dhul hijjah.