The Jataka, Vol. II, tr. by W.H.D. Rouse, , at sacred-texts.com
"Countless are my banners," etc.-- This story the Master told whilst living at Jetavana, about this same gadabout mendicant.
At that time, the Master, with a large company round him, sitting on the beautifully adorned throne of the truth, upon a vermilion dais, was discoursing like a young lion roaring with a lion's roar. The mendicant, seeing the Buddha's form like the form of Brahma, his face like the glory of the full moon, and his forehead like a plate of gold, turned round where he had come, in the midst of the crowd, and ran off, saying, "Who could overcome a man like this?"
The crowd went in chase, then came back and told the Master. He said, "Not only now has this mendicant fled at the mere sight of my golden face; he did the same before." And he told an old-world tale.
Once on a time, the Bodhisatta was king in Benares, and in Takkasilā reigned a certain king of Gandhāra. This king, desiring to capture Benares, went and compassed the city about with a complete army of four divisions. And taking his stand at the city gate, he looked upon his army, and said he, "Who shall be able to conquer so great an army as this?" and describing his army, he uttered the first stanza:--
 Then the Bodhisatta disclosed his own glorious countenance, in fashion as the full moon; and threatening him, thus spoke: "Fool, babble not vainly! Now will I destroy your host, as a maddened elephant crushes a thicket of reeds!" and he repeated the second stanza:
When the king of Gandhāra heard him threaten thus,  he looked up, and beholding his wide forehead like a plate of gold, for fear of being captured himself he turned and ran away, and came again even unto his own city.
This discourse ended, the Master identified the Birth:--"The vagrant gadabout was at that time the king of Gandhāra, and the king of Benares was I myself."