Śatapatha Brāhmaṇa ("of a hundred paths") 3.6.4.10

3.6.4.10

atha darbhataruṇakamantardadhāti | oṣadhe trāyasveti vajro vai paraśustatho hainameṣa vajraḥ paraśurna hinastyatha paraśunā praharati svadhite mainaṃ hiṃsīriti vajro vai paraśustatho hainameṣa vajraḥ paraśurna hinasti

He then places a blade of darbha-grass between, with, 'O plant, shield it!' for the axe is a thunderbolt; but thus that thunderbolt, the axe, does not hurt it (the tree). He then strikes with the axe, with, 'O axe, hurt it not!' for the axe is a thunderbolt, but thus that thunderbolt, the axe, does not hurt it.