Jaiminīya Upaniṣad Brāhmaṇa 2.12.3

2.12.3

ya u ha vā evaṃvidam ṛcchati yathaitā devatā ṛtvā nīyād evaṃ nyeti
etāsu hy evainaṃ devatāsu prapannam etāsu vasantam upavadati /

And whoever offends one who knows thus, just as if one were to perish having collided with these deities, so does he perish. For he speaks ill of him who has taken refuge in these deities, who dwells in them.