大乘起信論裂網疏 1.70

1.70

此謂眾生現前介爾之心即是如來藏也。夫真如不變隨緣，舉體而為眾生介爾之心，則介爾心便是真如全體。今又名為如來藏者，是約生滅門中，隱名如來藏、顯名法身故也。然法身與如來藏，雖有二名，終無二體，故不唯顯名法身之時，具足無量無邊性功德相，即正在隱名如來藏時，本來具足無量無邊性功德也。

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.