CHĀNDOGYA UPANISHAD · 1.2.13

तेन तं ह बको दाल्भ्यो विदां चकार ।
स ह नैमिशीयानाम् उद्गाता बभूव ।
स ह स्मैभ्यः कामान् आगायति ॥

tena taṃ ha bako dālbhyo vidāṃ cakāra ।
sa ha naimiśīyānām udgātā babhūva ।
sa ha smaibhyaḥ kāmān āgāyati ॥

Therefore Vaka Dâlbhya knew it. He was the Udgâtri (singer) of the Naimishîya-sacrificers, and by singing he obtained for them their wishes.

F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)