Shatapatha Brahmana 4.6.8.1

4.6.8.1

yā vai dīkṣā sā niṣat | tatsattraṃ tasmādenānāsata ityāhuratha yattato yajñaṃ tanvate tadyanti tannayati yo netā bhavati sa tasmādenānyantītyāhuḥ

Now the consecration-ceremony (for the sacrificial session) is a sitting down, is a session (sattra): hence they say of them, 'they sit.' And when thereafter they perform the sacrifice, then they (under)go; then he, who is the leader, leads: hence they say of them, 'they (under)go.'