You can find this exercise on page 15 of the book Synergistic Golf.
Exercise Type: PRE-ROUND WARMUP
Exercise Category: FLEXIBILITY, HIPS, LEGS - FEET
Supported with club or cart, bring right foot forward with weight remaining in heel. Reach left leg back far enough so heel is unable to touch down. Keep center of gravity between both legs and dip back knee down toward the floor. Focus on tall posture and navel pulled to spine.