大乘起信論別記 1.51

1.51

「覺知前念起惡」者，是所覺相，未入此位以前具起七支惡業，今入十信，即知前惡實是不善，故言覺知前念起惡。此明覺於滅相義也。

"Awakening to the previous thought having arisen as evil" is the characteristic that is awakened to. Before entering this stage, one fully produced the evil karma of the seven branches; now entering the ten faiths, one immediately knows that the previous evil was truly unwholesome, and hence it is said, "awakening to the previous thought having arisen as evil." This clarifies the meaning of awakening to the characteristic of ceasing.