Śatapatha Brāhmaṇa ("of a hundred paths") 9.3.3.13

9.3.3.13

dvādaśa kalpānjuhoti | dvādaśa māsāḥ saṃvatsaraḥ saṃvatsaro 'gniryāvānagniryāvatyasya mātrā tāvataivāsminnetatkLptānprāṇāndadhāti yadveva kalpānjuhoti prāṇā vai kalpā amṛtamu vai prāṇā amṛtenaivainametadabhiṣiñcati

Twelve prospering (libations) he offers,--a year consists of twelve months, and Agni is the year: as great as Agni is, as great as is his measure, by so much he thus puts proper vital airs into him. And as to why he offers the prospering (libations),--the prospering (libations) are vital airs, and the vital airs are the immortal element: with the immortal element he thus consecrates him.