首楞嚴義疏注經 6.151

6.151

The “samādhi of perfect illumination” is the one-practice samādhi. That is, initially conditioning upon the true mark, the realm one encounters is immediately the middle, and nothing is not true reality. Fastening the mind to the dharmadhātu, a single thought is the dharmadhātu; hence it is said, “my conditioned mind became free.” This is the Śūraṅgama concentration that is the central theme of the entire sūtra, the true perfect penetration praised by Mañjuśrī, which all buddhas celebrated together with interlocking rays of light upon this explanation. Later students reaching this point should, fortunately, pay close attention and not consider it of slight consequence.