Shatapatha Brahmana 1.6.4.8

1.6.4.8

tadvā etat samānameva satpaya eva sadindrasyaiva sattatpunarnānevācakṣate yadabravīddhinoti meti tasmāddadhyatha yadenaṃ śṛtenaivāśrayaṃstasmācūtaṃ

Now although this (mixture of sweet and sour milk) is, indeed, one and the same substance--it being milk (payas) and belonging to Indra--they, nevertheless, declare it to be (two) different (substances). Since he said 'it satiates (dhî) me,' therefore it is sour milk (dadhi); and since they made it agree (sri) with him with boiled milk (or, by boiling), therefore it is (fresh) boiled milk (srita).