CHĀNDOGYA UPANISHAD · 1.10.11

एवम् एव प्रतिहर्तारम् उवाच ।
प्रतिहर्तर् या देवता प्रतिहारम् अन्वायत्ता तां चेद् अविद्वान् प्रतिहरिष्यसि मूर्धा ते विपतिष्यतीति ।
ते ह समारतास् तूष्णीम् आसां चक्रिरे ॥

evam eva pratihartāram uvāca ।
pratihartar yā devatā pratihāram anvāyattā tāṃ ced avidvān pratihariṣyasi mūrdhā te vipatiṣyatīti ।
te ha samāratās tūṣṇīm āsāṃ cakrire ॥

In the same manner he addressed the Pratihartri: 'Pratihartri, if you, without knowing the deity which belongs to the pratihâra (the hymns of the Pratihartri), are going to sing it, your head will fall off.' They stopped, and sat down in silence.

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