瑜伽論記 2.62

2.62

Regarding 'the fourth dhyāna experiences the pleasure of purity of equanimity and mindfulness, which is tranquil and unmoving': because it is free from the eight disturbing dharmas that are coarse and defiled in the lower [three] dhyānas—that is, the first dhyāna is free from sorrow; the second dhyāna is free from investigation, reflection, and suffering; the third dhyāna is free from joy; and the fourth dhyāna is free from pleasure as well as inhalation and exhalation—it is therefore called tranquil and unmoving. 'Purity of equanimity' means that because it transcends all disturbances of investigation, reflection, joy, pleasure, and the like in the lower three dhyānas, the mind has the nature of equality, the nature of uprightness, and the nature of abiding securely without moving or turning. 'Purity of mindfulness' means that because it transcends all those disturbances, the mind is unforgetting and lucid. These two are supreme, which is why they are specifically mentioned.