Śatapatha Brāhmaṇa ("of a hundred paths") 1.6.4.1

1.6.4.1

indro ha yatra vṛtrāya vajram prajahāra | so 'balīyānmanyamāno nāstṛṣītīva bibhyannilayāṃ cakre sa parāḥ parāvato jagāma devā ha vai vidāṃ cakrurhato vai vṛtro 'thendro nyaleṣṭeti

When Indra had hurled the thunderbolt at Vritra, thinking himself to be the weaker, and fearing lest he had not brought him down, he concealed himself and went to the farthest distances. Now the gods knew that Vritra had been slain and that Indra had concealed himself.