Shatapatha Brahmana 9.1.2.32

9.1.2.32

athainaṃ sāmabhiḥ parigāyati | atraiṣa sarvo 'gniḥ saṃskṛtastasmindevā etadamṛtaṃ rūpamuttamamadadhustathaivāsminnayametadamṛtaṃ rūpamuttamaṃ dadhāti sāmāni bhavanti prāṇā vai sāmānyamṛtamu vai prāṇā amṛtamevāsminnetadrūpamuttamaṃ dadhāti sarvataḥ parigāyati sarvata evāsminnetadamṛtaṃ rūpamuttamaṃ dadhāti

[The Adhvaryu] then sings hymns round it (the altar);--for therein that whole Agni is completed; and the gods laid into him that highest form, immortality; and in like manner does this (Sacrificer) thereby lay into him that highest form, immortality. Sâman-hymns are (used), for sâmans are vital airs, and the vital airs are immortality: immortality, that highest form, he thus lays into him. On every side he sings around it: everywhere he thus lays immortality, that highest form, into him.