Aitareyabrahmana 4.2

4.2

gaurivītaṃ ṣoḷaśi sāma kurvīta tejaskāmo brahmavarcasakāmas.
tejo vai brahmavarcasaṃ gaurivītaṃ, tejasvī brahmavarcasī bhavati
ya evaṃ vidvān gaurivītaṃ ṣoḷaśi sama kurute
nānadaṃ ṣoḷaśi sāma kartavyam, ity āhur.
Indro vai Vṛtrāya vajram udayachat, tam asmai prāharat, tam abhyahanat.
so 'bhihato vyanadad.
yad vyanadat, tan nānadaṃ sāmābhavat, tan nānadasya nānadatvam.
abhrātṛvyaṃ vā etad bhrātṛvyahā sāma yan nānadam
abhrātṛvyo bhrātṛvyahā bhavati ya evaṃ vidvān nānadaṃ ṣoḷaśi sāma kurute
tad yadi nānadaṃ kuryur, avihṛtaḥ ṣoḷaśī śaṃstavyo;
'vihṛtāsu hi tāsu stuvate.
yadi gaurivītaṃ, vihṛtaḥ ṣoḷaśī śaṃstavyo;
vihṛtāsu hi tāsu stuvate

iv. 2 (xvi. 2). He who desires brilliance and splendour should use as the Ṣoḍaçin Sāman the Gaurivīta; the Gaurivīta is brilliance and splendour; brilliant and resplendent he becomes who knowing thus uses the Gaurivīta as Ṣoḍaçin Sāman. 'The Nānada should be used as the Ṣoḍaçin Sāman'

they say; Indra lifted up his thunderbolt against Vṛtra; he hurled it at him; he smote him. He, being smitten, cried aloud; in that he cried aloud, the Nānada Sāman came into existence; that is why the Nānada has its name. That is a Sāman without rivals, one that destroys rivals, the Nānada; without rivals, a destroyer of rivals, he becomes who, knowing thus, uses the Nānada as the Ṣoḍaçin Sāman. If they use the Nānada, the Ṣoḍaçin must be recited without intermingling; for they chant to the (verses) without intermingling. If it is the Gaurivīta, the Ṣoḍaçin must be recited with intermingling, for they chant to them with intermingling.