CHĀNDOGYA UPANISHAD · 1.11.8

अथ हैनं प्रतिहर्तोपससाद ।
प्रतिहर्तर् या देवता प्रतिहारम् अन्वायत्ता तां चेद् अविद्वान् प्रतिहरिष्यसि मूर्धा ते विपतिष्यतीति मा भगवान् अवोचत् ।
कतमा सा देवतेति ॥

atha hainaṃ pratihartopasasāda ।
pratihartar yā devatā pratihāram anvāyattā tāṃ ced avidvān pratihariṣyasi mūrdhā te vipatiṣyatīti mā bhagavān avocat ।
katamā sā devateti ॥

Then the Pratihartri approached him, saying: 'Sir, you said to me, "Pratihartri, if you, without knowing the deity belonging to the pratihâra, are going to sing it, your head will fall off,"--Which then is that deity?'

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