Shatapatha Brahmana 10.5.1.2

10.5.1.2

sā vā eṣā vāktredhāvihitā ṛco yajūṃṣi sāmāni tenāgnistredhāvihita etena hi trayeṇa cīyate'pyahaivaṃ tredhāvihita itthaṃ ha tvevāpi tredhāvihito yadasmiṃstredhāvihitā iṣṭakā upadhīyante puṃnāmnya strīnāmnyo napuṃsakanāmnyastredhāvihitānyu evemāni puruṣasyāṅgāni puṃnāmāni strīnāmāni napuṃsakanāmāni

Now, this speech is threefold--the Rik-verses, the Yagus-formulas, and the Sâman-tunes;--thereby the Fire-altar is threefold, inasmuch as it is built with that triad. Even thus, then, it is threefold; but in this respect also it is threefold, inasmuch as three kinds of bricks are put into it--those with masculine names, those with feminine names, and those with neuter names; and these limbs of men also are of three kinds--those with masculine names, those with feminine names, and those with neuter names.