佛說觀佛三昧海經 3.36

3.36

The Buddha said to his father the king and instructed Ānanda: "I shall now reveal in full to you the marks and rays of the body." Having spoken these words, the Buddha arose from his seat and said to Ānanda: "All you monks and Śākya sons! All of you arise, place your palms together facing the Buddha, and attentively contemplate the Tathāgata, from the light of the crown down to the light of the feet, and from the uṣṇīṣa on the crown down to the flat, full marks under the feet." He further instructed the monks: "Again, from the flat, full marks under the feet upward to the uṣṇīṣa, also contemplate the Tathāgata's bodily light and the light of his neck." He further instructed: "From each and every pore of the Buddha throughout the entire body, contemplate each detail distinctly, like a person holding a mirror and viewing the reflection of their own face. If one gives rise to defiled, evil, and unwholesome thoughts, or if one has violated the Buddha's prohibitive precepts, one will see the image as purely black, like a person made of charcoal."