Jaiminīya (Talavakāra) Brāhmaṇa 30.181.p3

30.181.p3

atha santani
yathā ha vai vyokasau vicchidya vyutkrāmata evaṃ ṣaṣṭhaṃ ca saptamaṃ cāhanī
vyucchidya vyutkāmataḥ
sa yathāśvaṃ saṃyojanena saṃyujyādevamatra santati
tasya sakṛtprastauti | triḥ pratiharati | trirnidhanamupayanti
tatsapta saṃpadyante saptamasyāhno rūpaṃ | saptarātrasya santatyā avyavacchedāya

Now the Santani sāman. Just as two men without a common abode separate and depart, so the sixth and seventh days separate and depart. Just as one would join a horse with a harness, so here is the Santani. Of it he sings the prelude once, he chants the response thrice, they chant the finale thrice. These amount to seven, the form of the seventh day, for the continuity of the seven-day period, for non-interruption.