大乘起信論別記 1.43

1.43

「離念相者，等虛空界」者，非唯無闇，無闇即是智惠，光明遍照法界平等無二故。言等虛空界，如下言「智惠光明義故，遍照法界義故。」

As for "the characteristic of being free from thought is equal to the realm of empty space," it is not only that it lacks darkness: the absence of darkness is precisely wisdom, and its light universally illuminates the dharmadhātu in equality without duality. Saying that it is equal to the realm of empty space is as stated below: "Because of the meaning of the light of wisdom, because of the meaning of universally illuminating the dharmadhātu."