Shatapatha Brahmana 13.5.1.2

13.5.1.2

tasya haike agniṣṭomasāma catuḥsāma kurvanti nāgniṣṭomo nokthya iti vadantastadyadi tathā kuryuḥ sārdhaṃ stotriyaṃ śastvā sārdhamanurūpaṃ śaṃsedrathantaram pṛṣṭhaṃ rāthantaraṃ śastramagniṣṭomo yajñastenemaṃ lokamṛdhnoti

Now, some make its Agnishtoma-sâman a Sâman of four (verses), saying, 'It is neither an Agnishtoma, nor an Ukthya.' If they do so, let hire (the Hotri), after reciting the Stotriya (strophe) together, recite the Anurûpa (strophe) together: the Rathantara Prishtha-sâman, the Sastra containing the Rathantara (text), and the Agnishtoma sacrifice--thereby he makes sure of this world.