俱舍論記 22.172

22.172

「論曰至阿波那念」者，釋息念。此即釋名。阿那，此云持來。阿波那，此云遣去。應名息慧而名念者，慧由念助力觀此息為境，名持息念。念能持息，名持息念。餘文可知。

The words 'The treatise says ... apāna-smṛti' explain mindfulness of breathing. This explains the name. Āna is translated here as 'drawing in'. Apāna is translated here as 'sending forth'. It ought to be named 'wisdom regarding breath', but is named 'mindfulness' because wisdom, aided by the power of mindfulness, contemplates this breath as its object; hence it is called 'mindfulness of breathing' (ānāpānasmṛti). Mindfulness being able to hold the breath is called mindfulness of breathing. The rest of the text is known [from context].