You can find this exercise on page 85 of the book Synergistic Golf.
Exercise Type: PRE-ROUND WARMUP
Exercise Category: ARMS - HANDS, FLEXIBILITY, LEGS - FEET
Place both palms against wall with arms out-stretched at shoulder level. Maintain upright posture and step-extend one leg back behind you so the heel can touch the floor. Lean gently forward into hands with body weight while maintaining back heel on ground with stretching feeling in back of lower leg. Repeat other leg holding for 10-20 seconds each.