Śatapatha Brāhmaṇa ("of a hundred paths") 4.5.4.13

4.5.4.13

tānvai pṛṣṭhye ṣaḍahe gṛhṇīyāt | pūrve tryaha āgneyameva prathame 'hannaindraṃ dvitīye sauryaṃ tṛtīya evamevānvaham

Let him draw them on the first three days of the Prishthya shadaha; namely, the Agni cup on the first day, the Indra cup on the second, the Sûrya cup on the third--thus one day by day.