Kena Upanishad 3.10

3.10

1.3.10
tasmai tṛṇaṃ nidadhāvetadādatsveti tadupapreyāya sarvajavena tanna śaśākādātuṃ sa tata eva nivavṛte naitadaśakaṃ vijñātuṃ yadetadyakṣamiti ||

23. That placed a straw before him and said “Blow it away.” He approached it with all speed but was not able to blow it. He returned immediately from there and told the Devas “I was not able to learn who this Great Spirit is.”