Atharvaveda 2.5.7

2.5.7

vr̥ṣāyámāṇo avr̥ṇīta sómaṃ tríkadrukeṣu apibat sutásya |
ā́ sā́yakaṃ maghávādatta vájram áhann enaṃ prathamajā́m áhīnām ||7||

Acting like a bull, he chose the soma; he drank of the pressed [draught] in the tríkadrukas; the bounteous one (maghávan) took his missile thunderbolt; he slew that first-born of dragons.