Not Yuvraj but Shastri is the 1st Indian to hit 6 sixes in an over

Ravi Shastri is the first Indian cricketer to hit 6 sixes in an over in any format of the cricket equaled the record of Sir Gary Sobers’s First-Class record of scoring 6 sixes in an over.  

Ravi Shastri while playing for Bombay against Baroda scored 36 runs in 6 balls and went on to score the fastest-ever double century in First-Class cricket history. He scored 200* in just 123 balls with the help of 13 sixes and 13 fours.

This record was touched by Yuvraj Singh in 2007 T-20 world cup vs England when he hit Stuart Broad for 6 sixes in an over and hit the fastest fifty in T20 international cricket.