佛說觀佛三昧海經 2.39

2.39

The Buddha told his father the king: “Regarding the Tathāgata’s white hair, from its first arising up to his attainment of buddhahood, the subtle and minor matters between them may be observed and contemplated. Once he had attained buddhahood, the light of the white ūrṇā was complete with all marks, as the Buddha has already explained extensively in the sūtras. The ultimate reach of the light of the white ūrṇā mark can only then be seen by bodhisattvas of the tenth ground; the minor aspects were spoken first, as these are easy for the world to see.”