CHĀNDOGYA UPANISHAD · 1.10.9

प्रस्तोतर् या देवता प्रस्तावम् अन्वायत्ता तां चेद् अविद्वान् प्रस्तोष्यसि मूर्धा ते विपतिष्यतीति ॥

prastotar yā devatā prastāvam anvāyattā tāṃ ced avidvān prastoṣyasi mūrdhā te vipatiṣyatīti ॥

'Prastotri, if you, without knowing the deity which belongs to the prastâva (the hymns &c. of the Prastotri), are going to sing it, your head will fall off.'

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