Yogācārabhūmi-śāstra: Volume 34 (46)

Thus, the practitioner, regarding the formations conducive to pleasant feelings and within the pleasant feelings themselves, enters into the suffering of change by observing the bonding formations. Regarding the formations conducive to painful feelings and within the painful feelings themselves, enters into the suffering of suffering by observing the disagreeable formations. Regarding the formations conducive to neither-painful-nor-pleasant feelings and within the neither-painful-nor-pleasant feelings themselves, enters into the suffering of conditioned existence by observing the unstable formations. Thus, due to the enhanced power of observing the bonding formations, the disagreeable formations, and the unstable formations, it is said regarding the three feelings: "All feelings are suffering." This is called: beginning with the mental application of the characteristic of impermanence, one enters into the observation of suffering.

Explanation: Thus, the yoga practitioner, in the formations conducive to pleasant feelings and within the pleasant feelings, by observing the bonding formations, enters into the observation of the suffering of change. In the formations conducive to painful feelings and within the painful feelings, by observing the disagreeable formations, enters into the observation of the suffering of suffering. In the formations conducive to neither-painful-nor-pleasant feelings and within the neither-painful-nor-pleasant feelings, by observing the unstable formations, enters into the observation of the suffering of conditioned existence. Thus, due to the enhanced power of mental application through observing the bonding formations, the disagreeable formations, and the unstable formations, the conclusion is reached within the three feelings: "All feelings are entirely suffering." This is called: beginning with the mental application of the characteristic of impermanence, it is for the purpose of first entering into the observation of suffering.