大乘起信論裂網疏 4.109

4.109

猶如迷人謂東為西，方實不轉。眾生亦爾，無明迷故，謂心為動，而實不動。若知動心即不生滅，即得入於真如之門。

It is like a lost person who takes east to be west, while the direction has not actually shifted. Sentient beings are also like this: because they are deluded by avidya, they take the mind to be moving, yet it is actually unmoving. If one knows that the moving mind is itself neither arising nor ceasing, one will then enter the gate of tathatā.