大乘起信論裂網疏 1.70

1.70

This means that the momentary mind present right before sentient beings is precisely the tathāgatagarbha. As tathatā accords with conditions yet is immutable, completely embodying itself as the momentary mind of sentient beings, this momentary mind is none other than the entire essence of tathatā. The reason it is now also named 'tathāgatagarbha' is that, in terms of the aspect of arising and ceasing, when concealed it is named tathāgatagarbha, and when revealed it is named dharmakāya. However, although dharmakāya and tathāgatagarbha have two names, ultimately they have no two essences. Therefore, not only when it is revealed and named dharmakāya does it possess boundless, limitless attributes of innate merit, but even precisely when concealed and named tathāgatagarbha, it originally possesses boundless, limitless innate merits.