佛說觀佛三昧海經 3.7

3.7

“How does one contemplate the mark of the Tathāgata’s lion yawn? When the Buddha opens his mouth, it is square and even like that of a lion king. From both corners of the mouth flow forth three rays of light; their golden color exceeds the previous light by hundreds of thousands of ten millions of times, ascending into the light of the ears, circling the hair, and emerging from the occipital bone to circle the preceding halo. Between each line there are three transformation Buddhas; each transformation Buddha has two Brahmā kings as attendants. This is called the mark of the Tathāgata’s lion yawn.”