首楞嚴義疏注經 7.198

7.198

銷散為緣，惑暗顛倒，厭壞色相，思無邊空。色盡心亡，厭空絕想，乃至有頂沈冥幽隱，即無色界外道之類耳。

Taking dissolution as the condition, with deluded, dark inversion, they tire of and destroy form, contemplating boundless space. When form is exhausted and the mind is extinguished, they tire of space and sever thought, sinking down into obscurity even up to the peak of existence; these are the heterodox beings of the formless realm.