You can find this exercise on page 87 of the book Synergistic Golf.
Exercise Type: DYNAMIC STRETCH
Exercise Category: BALANCE, HIPS, STRENGTH
Stand tall. Shift weight onto right leg maintaining posture and hip alignment. Try to balance lifting left leg off floor out to the side. If balance can be maintained, continue lifting left leg in and out 10x then switch sides. Repeat 10x each side for 3 sets.