首楞嚴義疏注經 5.266

5.266

須菩提，云空生，亦善現等，以生時現空，心達於空，常修空行，故以為名。既云曠劫如恒河沙，便知空寂，豈止今日方始證得。

Subhūti is translated as 'Born from Emptiness', and also as 'Good Appearance', etc. Because at his birth emptiness manifested, his mind penetrated emptiness, and he constantly cultivated the practice of emptiness, he was so named. Since he says that for kalpas as numerous as the sands of the Ganges he already knew emptiness and tranquility, how could it be that only today did he first realize it?