Kena Upanishad 3.6

3.6

1.3.6
tasmai tṛṇaṃ nidadhāvetaddaheti| tadupapreyāya sarvajavena tanna śaśāka dagdhaṃ sa tata eva nivavṛte naitadaśakaṃ vijñātuṃ yadetadyakṣamiti ||

not consume it. He returned from the Yakṣa (to tell the gods), "I could not ascertain It fully as to what this Yakṣa is."

Tasmai, for him, who had such presumption: Brahman tṛṇam nidadhau, placed a straw, in front of Fire. Being told by Brahman, "Etat, this, mere straw; daha, burn, in my front. If you are not able to burn it, give up your vanity as a consumer everywhere." (Fire) tat upapreyāya, went near that straw; sarvajavena, with the speed born of the fullest enthusiasm. Going there, tat, that thing; na śaśāka dagdhum, he could not burn, That Fire being unable to burn the straw and becoming ashamed and foiled in his promise, tataḥ eva, from that Yakṣa; silently nivavṛte, withdrew, and went back towards the gods (to tell them), "Na aśakam, I did not succeed; vijñātum, in knowing fully, etat, this Yakṣa: yat etat Yakṣam, as to what this Yakṣa is."