Jaiminīya Upaniṣad Brāhmaṇa 2.3.13

2.3.13

sa yathāśmānam ākhaṇam ṛtvā loṣṭo vidhvaṁsata evam eva sa vidhvaṁsate ya evaṃ vidvāṁsam upavadati /
dvitīye 'nuvāke prathamaḥ khaṇḍaḥ //

Just as a clod of earth having struck a solid stone shatters, so indeed shatters he who speaks ill against one who knows thus.
First khaṇḍa in the second anuvāka.