佛說觀佛三昧海經 1.61

1.61

佛告父王：「是名菩薩出家時白毛相種種瑞應。若佛滅後諸四部眾，欲觀如來出家時白毛相者，當作是觀，若異觀者是名邪觀。」

The Buddha said to his father the king: "These are called the various auspicious omens of the Bodhisattva's white-hair mark at the time of going forth. If, after the Buddha's extinction, members of the fourfold assembly wish to contemplate the mark of the Tathāgata's white hair at the time of going forth, they should contemplate in this way. Contemplating otherwise is called false contemplation."