Sanskrit

अपाने जुह्वति प्राण प्राणेऽपानं तथाऽपरे। प्राणापानगती रुद्ध्वा प्राणायामपरायणाः।।4.29।।

Summary

There are some who practice controlling the vital energy and governing the subtle forces of prana and apana, thereby sacrificing their prana to apana, or their apana to prana.