俱舍論記 22.173

22.173

「以慧為性至如念住故」者，釋慧，此即出體。此持息念以慧為性，而說念者，此品念勝故得念名，由念力記持入出息量故，慧於境分明所作事成故，如四念住以慧為體而言念住。

The words 'Having wisdom as its intrinsic nature ... as in the foundations of mindfulness' explain wisdom; this identifies the essence. This mindfulness of breathing has wisdom as its nature; yet it is spoken of as mindfulness because mindfulness is superior in this category and thus receives the name of mindfulness; because by the power of mindfulness one remembers and holds the measure of inhalation and exhalation, wisdom is clear regarding the object and its task is accomplished, just as the four foundations of mindfulness have wisdom as their essence yet are spoken of as foundations of mindfulness.