Śatapatha Brāhmaṇa ("of a hundred paths") 1.6.4.9

1.6.4.9

sa yathāṃśurāpyāyet | evamāpyāyatāpa pāpmānaṃ harimāṇamahataiṣa u āmāvāsyasā bandhuḥ sa yo haivaṃ vidvāntsaṃnayatyevaṃ haiva prajayā paśubhirāpyāyate 'pa pāpmānaṃ hate tasmādvai saṃnayet

In the same way as the Soma stalk becomes strong (by being touched or sprinkled with water), so he (Indra) became strong (by the Soma being mixed with boiled milk) and overcame that evil, the jaundice. Such is likewise the significance of the new-moon ceremony (and the Sânnâyya, or libation of sweet and sour milk offered to Indra thereat); and verily he who, knowing this, mixes (sweet and sour milk at the new-moon sacrifice) in like manner increases in offspring and cattle, and overcomes evil: let him therefore mix together (sweet and sour milk).