As the Shatapatha Brahmana tells it
Shatapatha Brahmana 1.4.1 · 3 min read
King Mathava of Videgha lived on the banks of the river Sarasvati, and he had an odd habit. He did not talk.
His people may have thought him proud. His family priest, the sage Gotama Rahugana, knew better. The king was carrying something in his mouth and was afraid it would fall out. He was carrying Agni Vaishvanara, the sacred fire that belongs to all people.
One day the priest spoke to him and got no answer.
"Mathava!"
Nothing. The king kept his lips pressed shut.
Gotama decided to speak to the fire directly. He recited a verse of the Rigveda in praise of Agni, the wise one, the bright one, kindled at the sacrifice. Then he called again.
"O Videgha!"
The king said nothing.
The priest tried a second verse. "Upward, O Agni, rise your flames, your bright and shining lights!" And again: "O Videgha!"
Still the king said nothing, though this time, you may imagine, he was holding on a little harder.
So the priest began a third verse. "You, O butter-sprinkled one, we call upon..."
He got no further. The word butter had hardly left his lips when Agni blazed up. Fire loves butter above everything, and he could not stay hidden when he heard it named. The king could not hold him. The fire burst out of his mouth and fell to the ground.
He did not stay where he fell. He began to move east.
He went burning along the earth, and the priest and the king ran after him. He burnt his way across the land, and when he came to a river he burnt across that too and dried it up. One river after another he crossed in this way.
Then he came to a river called the Sadanira, which flows down from the northern mountains. And at this one river he stopped. He did not burn over it.
On the far bank the land was wild. It was marshy and untilled, because fire had never tasted it. No brahmin in those days would cross the Sadanira, the old book says, for that very reason.
King Mathava stood on the bank, out of breath, and now that his mouth was empty he could speak at last. He asked the fire a plain question.
"Where am I to live?"
"To the east of this river," said Agni. "Let that be your home."
So the king crossed over. The book adds that in its own day that river was still the border between two peoples, the Kosalas on one side and the Videhas on the other. It adds that the land beyond it had long since become good farmland, full of brahmins, because they had brought the fire across and let Agni taste the ground through their sacrifices. And it says the river still ran cold in the hottest part of summer, since Agni never burnt it.
When it was all over, the priest turned to his king.
"I called you three times. Why did you not answer?"
"Agni Vaishvanara was in my mouth," said Mathava. "I was afraid he would fall out. So I kept quiet."
"And how did it happen, in the end?"
"The moment you said butter," said the king, "he flashed out. I could not hold him."