佛說觀佛三昧海經 4.6

4.6

佛告父王：「云何名為觀於如來眉間光明？如來今者，為此後世諸眾生故，當少現於白毫相光。」

The Buddha said to his father the king: "What is called contemplating the light between the Tathāgata's eyebrows? For the sake of all sentient beings of future generations, the Tathāgata will now manifest a small portion of the light of the mark of the white curl between his eyebrows (ūrṇā)."