俱舍論頌疏論本 23.8

23.8

治倒故唯四者，此四念住，觀身不淨、觀受是苦、觀心無常、觀法無我，治彼常、樂、我、淨四顛倒故，故唯立四。論云：「四中三種唯名不雜緣，第四所緣通雜、不雜。若唯觀法，名不雜緣。若於身等二、三或四，總而觀察，名為雜緣。」解云：於身等四，或二二合緣、三三合緣、或四總緣，雜身等故，名雜緣也。

As for "Because they counter the distortions, there are only four": these four applications of mindfulness contemplate the body as impure, contemplate feelings as suffering, contemplate the mind as impermanent, and contemplate dharmas as non-self; because they counter the four distortions of permanence, pleasure, self, and purity, only four are established. The treatise says: "Among the four, three are named solely 'unmixed objective support', while the fourth's objective support extends to both mixed and unmixed. If one contemplates dharmas alone, it is named 'unmixed objective support'. If one contemplates two, three, or four of the body, etc., together, it is named 'mixed objective support'." Explanation: With respect to the four—body, etc.—either taking two together as object, three together as object, or all four collectively as object, because they mix the body and the rest, it is called 'mixed objective support'.