Shatapatha Brahmana 4.6.1.12

4.6.1.12

tāsāṃ dvādaśa garbhāḥ | tāścaturviṃśatiścaturviṃśatirvai saṃvatsarasyārdhamāsāḥ saṃvatsaraḥ prajāpatiḥ prajāpatiraṃśustadenam prajāpatiṃ karoti

They have twelve embryo calves,--that makes twenty-four. Now there are twenty-four half-moons in the year, and Pragâpati is the year, and the Amsu is Pragâpati: thus he makes him to be Pragâpati.