Śatapatha Brāhmaṇa ("of a hundred paths") 6.2.1.23

6.2.1.23

yadveva caturviṃśatiḥ | caturviṃśo vai puruśo daśa hastyā aṅgulayo daśa pādyāścatvāryaṅgāni puruṣaḥ prajāpatiḥ prajāpatiragniryāvānagniryāvatyasya mātrā tāvataivainametatsaminddhe

And, again, why there are twenty-four,--man (purusha) doubtless is twenty-fourfold: ten fingers of the hands, ten toes, and four limbs; and Pragâpati is the Purusha, and Pragâpati is Agni: as great as Agni is, as great as is his measure, by so much he thus kindles him.