Yogācārabhūmi-śāstra, Volume 34 (33)

Original text: 云何观察光明变异无常之性。谓由观见种种明闇。生灭变异。见此事已。便作是念。如是诸行。其性无常。余如前说。云何观察男女承奉所有变异无常之性。谓观见彼。或衰或盛。不久坚住。见此事已。便作是念。如是诸行。其性无常。余如前说。

Explanation: How does one observe the impermanent nature of the transformation of light? One sees the arising, ceasing, and transformation of various marks of brightness and darkness; after observing these phenomena, one then has this thought: such volitional formations are truly impermanent in nature. How does one observe the impermanent nature of the transformation of the mutual affection between men and women? One observes that the affection between men and women goes from flourishing to declining, and from declining to flourishing, and cannot last long; after observing these phenomena, one then has this thought: such volitional formations are truly impermanent in nature.