釋禪波羅蜜次第法門 7.51

7.51

復次，知久近：入息時近，出息時久。何以故？息入既利，則易盡，故近；息出澁，則難盡，故久。復須覺知因出入息故，則有一切眾苦煩惱，生死往來，輪轉不息，心知驚畏。行者隨息之時，知息有如是等法相非一，故云知息入出也。

Furthermore, knowing length of time: the inhalation is short, and the exhalation is long. Why is this? Since the in-breath enters swiftly, it is easily exhausted, and thus short; since the out-breath exits sluggishly, it is difficult to exhaust, and thus long. One must also become aware and know that because of inhalation and exhalation, all sufferings and afflictions exist, with coming and going in birth and death, revolving incessantly, such that the mind feels alarm and dread. When the practitioner follows the breath, he knows that the breath possesses various characteristics such as these that are not solitary; therefore it is said that he knows the inhalation and exhalation of the breath.