釋禪波羅蜜次第法門 7.50

7.50

復次，知澁滑：入息時滑，出息時澁。何以故？息從外來，風氣利故，則滑；從內出吹，內滓穢，塞諸毛孔，則澁。復次，知冷暖：知入息時冷，知出息時暖。何以故？息從外來，冷氣而入，故冷；息從內出，吹內熱氣而出，故暖。

Furthermore, knowing roughness and smoothness: during the in-breath it is smooth, and during the out-breath it is rough. Why is this? Since the breath comes from outside, the air is sharp, so it is smooth; blowing out from within, inner impurities block the pores, so it is rough. Furthermore, knowing cold and warmth: knowing that during the in-breath it is cold, and during the out-breath it is warm. Why is this? Since the breath comes from outside, cold air enters, so it is cold; when the breath exits from within, it blows out warm air from inside, so it is warm.