The Prashna Upanishad with Shankara’s Commentary
अरा इव रथनाभौ प्राणे सर्वं प्रतिष्ठितम् ।
ऋचो यजूँषि सामानि यज्ञः क्शत्रं ब्रह्म च ॥ ६ ॥
arā iva rathanābhau prāṇe sarvaṃ pratiṣṭhitam |
ṛco yajūm̐ṣi sāmāni yajñaḥ kśatraṃ brahma ca || 6 ||
6. As spokes in the nave of a wheel, so all is centred in Prâna. Riks, Yajur, Sâmams, sacrifices, Kshatriyas and Brâhmins.
Com.—As spokes in the nave of a wheel, all from sraddhâ (faith) down to name is centred in Prâna, while they endure; so also Rik, Yajur and Sâma Vêdâs, the three kinds of mantras, and what is accomplished by them, i.e., the sacrifice, the Kshatriyas, pro tectors of all and the Brahmins competent to perform sacrifices and other karma. Prâna is all this.