摩訶止觀 9.38

9.38

此樂對苦，呵樂即謝，亦有未到。未到謝已，發不動定，還是色法轉妙。不為苦樂所動，名「不動定」。定法安隱，出入息斷，不苦不樂、捨、念清淨、一心支。

This bliss stands opposed to suffering; reproaching bliss, it then subsides, and there is also a preparatory stage. When the preparatory stage has subsided, the immovable concentration manifests, which is still the material form becoming increasingly wondrous. Not being moved by suffering or bliss, it is called the 'immovable concentration.' The state of concentration is peaceful and stable; inhalation and exhalation cease; it has the factors of neither-suffering-nor-bliss, purity of equanimity and mindfulness, and one-pointedness of mind.