大乘起信論裂網疏 6.57

6.57

The "mark of the dharmadhātu" is the essence of tathatā—the real mark that has no mark and yet lacks no mark. Mind, Buddha, and sentient beings: these three are without distinction, hence it is named the "samādhi of one mark"; the Liang translation calls it the "samādhi of one practice". It is named "one mark" in terms of what is realized, and named "one practice" in terms of what can realize it; one should know that the one practice is just the one mark. The samādhi of one practice shown in the *Mañjuśrī-prajñā[pāramitā-sūtra]* is precisely identical with this; it is also the Śūraṅgama-king samādhi of the *Da foding [ruolai miyin xiuzheng liaoyi zhupusa wanxing shoulengyan jing]*, and likewise the real-mark samādhi of the *Lotus [Sūtra]*. This is the king among samādhis, and therefore can give birth to immeasurable samādhis.