You can find this exercise on page 219 of the book Synergistic Golf.
Exercise Type: YOGA-STRETCH
Exercise Category: FLEXIBILITY, HIPS, LEGS - FEET
Stand and kick left foot back into left hand. You may use your golf club for support in right hand. Press the knee back and hip forward of left leg to promote greater stretch and pull left heel to left buttock. Pull belly button in throughout stretch. Hold 10 seconds. Repeat other leg.