KeU 3.10
तस्मै तृणं निदधावेतदादत्स्वेति तदुपप्रेयाय सर्वजवेन तन्न शशाकादतुम् | स तत एव निववृते नैतदशकं विज्ञातुं यदेतद्यक्षमिति
Brahman placed a straw before him and said: "Blow this away." He (Vayu) rushed towards it with all speed, but was not able to blow it away. So he returned from there and said (to the Devas): "I was not able to find out what this great mystery is."
Translated by Swami Paramananda
Brahman put a straw before him, saying: 'Take it up.' He went towards it with all his might, but he could not take it up. Then he returned thence and said: 'I could not find out what sprite this is.'
Translated by F. Max Müller