Bhagavatapurana 4.19.30

4.19.30

na vadhyo bhavatām indro yad yajño bhagavat-tanuḥ /
yaṃ jighāṃsatha yajñena yasyeṣṭās tanavaḥ surāḥ //

30. Indra ought not to be killed by you, for Indra called Yagna is an avatār of the glorious Lord Hari; and he (Indra) whom you think of killing by means of the sacrifice is really the abode of all the gods whom you worship by sacrifices.