俱舍論頌疏論本 28.16

28.16

空無邊等三，名從加行立者，謂修定前起加行位，厭色境故，作勝解想，思無邊空加行成時，名空無邊處。又於加行中厭無邊空，起勝解想，思無邊識，加行成時，名識無邊處。又於加行中厭無邊識，起勝解想，捨諸所有寂然而住，加行成時，名無所有處。

Regarding "The three, such as boundless space, derive their names from preparation": this means that prior to cultivating concentration, in the preparatory stage, because one turns away from the objective realm of form, one forms an act of resolve and contemplates boundless space; when the preparation is accomplished, it is called the 'sphere of boundless space.' Furthermore, in preparation, turning away from boundless space, one forms an act of resolve and contemplates boundless consciousness; when the preparation is accomplished, it is called the 'sphere of boundless consciousness.' Furthermore, in preparation, turning away from boundless consciousness, one forms an act of resolve and abandons all possessions, abiding in stillness; when the preparation is accomplished, it is called the 'sphere of nothingness.'