Kauṣītaki (Śāṅkhāyana) Brāhmaṇa 4.6.13

4.6.13

sākam prasthāyyena iṣyann etasyām eva amāvāsyāyām prayuṅkte tasyā uktam brāhmaṇam / (Vikṛti iṣṭayah)

iv. 9. Next as to the Sākaṁprasthāyya sacrifice. He who means to proceed with the Sākaṁprasthāyya begins on the same new moon night; the explanation of it has been given. It is a sacrifice for one desiring pre-eminence, desiring heroism; with it should one desiring pre-eminence, desiring heroism, sacrifice. In that together they move forward, together they sacrifice, together they eat, therefore is it called Sākaṁprasthāyya (moving forward together).