The Upanishads - Mandhata Global

In the same manner he addressed the udgatri priest: "O
udgatri priest, if without knowing the deity that belongs
to the Udgitha, you sing the Udgitha, your head will fall
off."
In the same manner he addressed the pratihartri priest:
"O pratihartri priest, if without knowing the deity that
belongs to the Pratihara, you sing the Pratihara, your
head will fall off."
They all stopped performing their duties and sat in
silence.
429