Śatapatha Brāhmaṇa ("of a hundred paths") 8.6.2.2

8.6.2.2

tricānyupadadhāti | trivṛdvai paśuḥ pitā mātā putro 'tho garbha ulbaṃ jarāyuatho trivṛdvā annaṃ kṛṣirvṛṣṭirvījamekaivāticandā bhavatyekā hyeva sā sarvāṇi candāṃsyati sā yā sā śrīrmahattadukthaṃ tadyattanmahadukthametāstāścandasyāḥ

He lays down triplets, for the beast is threefold--father, mother, son; and, embryo, amnion, chorion; and food also is threefold--ploughing, rain, seed. One of them is an Atikhandas (excessive metre); for even whilst being one, that one is beyond all the metres. And as to that distinction, it is this great hymn of praise; and as to this great hymn of praise, it is these Khandasyâs.