You can find this exercise on page 74 of the book Synergistic Golf.
Exercise Type: YOGA-STRETCH
Exercise Category: FLEXIBILITY, HIPS, LEGS - FEET
Sit on floor and bring bottoms of feet together. Place elbows on knees while grabbing ankles. Apply gentle pressure with elbows on knees and feel tension and stretch in groin and hips. You may fly your knees up and down to increase circulation, but do not ballistically bounce.