You can find this exercise on page 245 of the book Synergistic Golf.
Exercise Type: PRE-ROUND WARMUP
Exercise Category: FLEXIBILITY, HIPS, LEGS - FEET
Begin kneeling on all fours. Step your left foot forward between your hands. Left ankle-knee-hip will form a 90 degree angle. Curl toes of back foot under pushing heel away from body. Lean body forward edging right thigh toward floor. Advanced: Put both elbows on floor inside of left foot. Repeat with right leg.