釋禪波羅蜜次第法門 5.38

5.38

二、明證未到地定相，因此欲界定後，身心泯然虛豁，失於欲界之身，坐中不見頭手床敷，猶若虛空，此是未到地定。所言未到地者，此地能生初禪故，即是初禪方便定，亦名未來禪，亦名忽然湛心。證此定時，不無淺深之相，今不具明。

Second, explaining the marks of realizing anāgamya concentration: following this desire-realm concentration, body and mind become serenely empty and open, losing the desire-realm body. While sitting, one does not see head, hands, or seat, just like empty space; this is anāgamya concentration. What is called "anāgamya" is because this stage can generate the first dhyāna; that is, it is the expedient concentration for the first dhyāna, also called future dhyāna, and also called the suddenly serene mind. When realizing this concentration, there are definitely marks of shallowness and depth, which will not be explained in full now.