首楞嚴義疏注經 5.260

5.260

有所得心一念不起，名之為攝。當爾之際，能覺所覺、能觀所觀一時俱寂，無分別智即得現前，證無生忍，故云身心忽空。

When a mind that seeks attainment does not arise for a single thought-moment, this is called 'gathering'. At that very moment, the perceiving and the perceived, the contemplating and the contemplated, were simultaneously tranquil. The non-conceptual wisdom thereupon manifested, realizing the forbearance of non-arising dharmas; hence it says, 'body and mind were suddenly empty.'