Taittiriyabrahmana 3.10.9.5

3.10.9.5

kásmin nú tápa íti /
bála íti /
kíṃ tád bálam íti /
prāṇá íti /
mā́ sma prāṇám átipṛccha íti mā_ācāryò 'bravīd íti ha_uvāca brahmacārī́ //
sá ha_uvāca plakṣó dáiyāmpātiḥ /
yád vái brahmacārin prāṇám atyáprakṣyaḥ /
mūrdhā́ te vyàpatiṣyat /
ahám u ta ācāryā́t_śréyān bhaviṣyāmi /
yó mā sāvitré samávādiṣṭa_íti /

"In what, now, is austerity [established]?"
"In strength."
"What is that strength?"
"Prāṇa."
"'Do not ask beyond prāṇa,' the teacher told me," said the student.
Plakṣa Dayyāmpāti said:
"Truly, student, if you had asked beyond prāṇa,
your head would have fallen off.
And I shall be better than your teacher,
who disputed with me concerning the Sāvitra!"