You can find this exercise on page 247 of the book Synergistic Golf.
Exercise Type: YOGA-STRETCH
Exercise Category: FLEXIBILITY, HIPS, LEGS - FEET, LOW BACK
Lie on your back with knees bent and feet flat on floor. Cross right ankle over left knee pointing right knee out to side. Reach hands around left thigh and pull legs off floor and knees toward chest. Relax the head. For added stretch, head may be lifted reaching chin toward legs with control. Hold 10 seconds and switch sides..