Ramayana
एकांशो वासवं यातु द्वितीयो वज्रमेव तु । तृतीयो भूतलं शक्रस्तदा वृत्रं वधिष्यति ॥ 7-85-7 ॥
"Let one portion enter Vasava (Indra), the second the thunderbolt, and the third the surface of the earth; then Shakra shall slay Vritra."
english translation