法界次第初門 2.147

2.147

二、受念處者，六觸因緣生六受，從六受生三受，名之為受。是中觀受智慧名為念。明達三受皆苦，破樂顛倒，即是處。觀外受、內外受亦如是，是為受念處也。

Second, mindfulness of feeling: the conditions of the six contacts generate the six feelings, and from the six feelings arise the three feelings, which are called feeling. Within this, the wisdom that contemplates feeling is called 'mindfulness'. Clearly penetrating that the three feelings are all suffering to shatter the inversion of pleasure is 'basis'. Contemplating external feelings and internal-and-external feelings is also like this. This is the mindfulness of feeling.