大乘起信論義記 2.131

2.131

下顯得中，若至心源得於無念則遍知一切眾生一心動轉四相差別，故言若得無念者，則知心生住異滅也。以無念等故者，釋成上義。

Below, in revealing the gain, if one reaches the source of the mind and attains thoughtlessness, then one comprehensively knows the differences of the four marks in the movements of the One Mind of all sentient beings; hence it says, 'if one attains thoughtlessness, then one knows the mind's arising, abiding, difference, and cessation.' 'Because of the equality of thoughtlessness' explains and establishes the above meaning.