Jaiminīya Upaniṣad Brāhmaṇa 2.1.6

2.1.6

te manasodgātrādīkṣanta
sa yad eva manasā dhyāyati tad ātmana āgāyad atha ya itare kāmās tān devebhyaḥ /

They consecrated themselves with the mind as the udgātṛ. Whatever one thinks with the mind, that he sang for himself, but whatever other desires there were, those [he sang] for the gods.