Yogācārabhūmi-śāstra, Volume 34 (21)

Original text:云何观察内事杂染。所作变异。无常之性。谓能了知。先所生起。或有贪心。或离贪心。或有瞋心。或离瞋心。或有痴心。或离痴心。又能了知。随一一种诸随烦恼。所染污心。又能了知。随一一种诸随烦恼。不染污心。又能了知。彼心相续。由诸烦恼及随烦恼。于前后位。趣入变坏不变坏性。见是事已。便作是念。如是诸行。其性无常。何以故。心由杂染所作变异。现可得故。

Explanation: How does one observe the impermanent nature of the changes wrought upon internal matters (bhūmi-vastu) by defilement? One is able to know the defiled minds that arose previously—whether there was a mind with greed or a mind free of greed; whether there was a mind with anger or a mind free of anger; whether there was a mind with delusion or a mind free of delusion. One is also able to know the defiled mind that arises with each and every one of the secondary afflictions, and one is also able to know the undefiled mind that arises with each and every one of the secondary afflictions. One is further able to know that, in the continuity of that defiled mind, through the various afflictions and secondary afflictions, one successively enters, in earlier and later stages, into the nature of either change and deterioration or non-change and non-deterioration. Having observed these phenomena, one gives rise to this thought in the mind: such volitional formations are truly impermanent in nature. Why? Because the changes wrought upon the mind by defilement can be directly observed in the present.