Shatapatha Brahmana 6.2.1.21

6.2.1.21

teṣāṃ caturviṃśatiḥ sāmidhenyaḥ | caturviṃśatyardhamāso vai saṃvatsaraḥ saṃvatsaro 'gniryāvānagniryāvatyasya mātrā tāvataivainametatsaminddhe

For these (victims) there are twenty-four kindling-verses; for the year consists of twenty-four half-moons, and Agni is the year: as great as Agni is, as great as is his measure, by so much he thus kindles him.