"The Śūraṅgama Sūtra, Volume Ten: The Subtle and Hidden Delusions of the Formations Aggregate"

Original: The transformations of the body never cease; ceaselessly and subtly shifts occur. Nails grow, hair sprouts, vital energy wanes, and the countenance wrinkles. Day and night, [these processes] succeed one another, yet there has never been any awareness of it. Ānanda, if this is not you, why does your body undergo change? If this is truly you, why are you unaware and unperceiving? Therefore, all your ceaselessly fleeting volitional formations are called the Fourth Obscure Delusion.

Explanation: The transformations of the body have never stopped; moment by moment, they are ceaselessly and subtly shifting and changing. For example, nails grow longer, hair sprouts, vital energy diminishes, the countenance wrinkles – the various functions of the body are renewed and replaced day and night, yet one has never been aware of it oneself. Ānanda, if these volitional formations are not you, why does your body undergo change? If these volitional formations are truly you, why are you unawakened and unaware? Therefore, all your ceaselessly fleeting volitional formations are called the Fourth Obscure Delusion.