Śāṅkhāyana (Kauṣītaki) Āraṇyaka 2.7

2.7

ŚĀ 2.7
Then he recites these [sets of] eighty [triplets]. With them he recites after the stotriyas: with the Gāyatrī [set] after the Gāyatra, and with the Auṣṇiha and Bārhata [sets] after the Bṛhat and Rathantara. This Gāyatrī is the right side, the Auṣṇihī the left, the Bārhatī the middle. For this food of the self is placed in the middle. Between two Triṣṭubhs is a Triṣṭubh nivad verse. Belonging to Viśvāmitra, containing the word arka, they are appropriate. For Viśvāmitra saw this. The opening verses contain mahat and contain vṛdh. They contain mahat and contain vṛdh; for this day has the character of mahat, of mahat.