Chāndogya Upaniṣad 4.17.6

4.17.6

atha yadi sāmato riṣyet svaḥ svāhety āhavanīye juhuyāt \
sāmnām eva tadrasena sāmnāṃ vīryeṇa sāmnāṃ yajñasya viriṣṭaṃ saṃdadhāti \\417.6\

6. Moreover, if there should come an injury in connection with the Sāman chants, one should make an oblation in the eastern (Āhavanīya) fire with the words '*svar*! Hail!' So by the essence of the Sāman chants, by the power of the Sāman chants he mends the injury to the Sāman chants of the sacrifice.