Brihadaranyaka Upanishad 3.1.7

3.1.7

yājñavalkyeti hovāca katibhirayamadyargbhirhotāsminyajñe kariṣyatīti tisṛbhiriti katamāstāstisra hati puro'nuvākyā ca yājyā ca śasyaiva tṛtīyākiṃ tābhirjayatīti yatkiṃ cedaṃ prāṇabhṛditi

'Yâgñavalkya,' he said, 'how many Rik verses will the Hotri priest employ to-day at this sacrifice?'
'Three,' replied Yâgñavalkya.
'And what are these three?'
'Those which are called Puronuvâkyâ, Yâgyâ, and, thirdly, Sasyâ.'
'What does he gain by them?'
'All whatsoever has breath.'