瑜伽論記 7.40

7.40

初中，言以一為一算數者，景云：初緣入息，不觀出息，故云出息住念。泰云：此但緣入息，然念從境立名，名入出息住念。

In the first part, regarding the statement 'counting one as one': Jing says that at first one takes the in-breath as object and does not contemplate the out-breath, which is why it is called 'mindfulness abiding in the out-breath'. Tai says that this takes only the in-breath as object; however, mindfulness is named after its object, hence it is called 'mindfulness abiding in the in-and-out breaths'.