Aitareyabrahmana 4.2

4.2

One who desires splendour, who desires priestly lustre, should make the Gaurivīta the sāman of the ṣoḷaśin.
The Gaurivīta is splendour and priestly lustre; he becomes splendid and endowed with priestly lustre
who, knowing thus, makes the Gaurivīta the sāman of the ṣoḷaśin.
They say: 'The Nānada is to be made the sāman of the ṣoḷaśin.'
Indra raised the thunderbolt against Vṛtra; he hurled it at him; he struck him down.
He, when struck, roared aloud.
Because he roared aloud (vyanadat), that became the Nānada sāman; that is the Nānada-ness of the Nānada.
This sāman, the Nānada, is free from rivals and slays rivals;
free from rivals, a slayer of rivals he becomes who, knowing thus, makes the Nānada the sāman of the ṣoḷaśin.
In that case, if they should use the Nānada, the ṣoḷaśin is to be recited un-interwoven;
for upon those [verses] un-interwoven they chant.
If the Gaurivīta, the ṣoḷaśin is to be recited interwoven;
for upon those [verses] interwoven they chant.