Śatapatha Brāhmaṇa ("of a hundred paths") 3.3.1.15

3.3.1.15

sā yā babhruḥ piṅgākṣī | sā somakrayaṇī syādyadi babhrum piṅgākṣīṃ na vindedaruṇā syādyadyaruṇāṃ na vindedrohiṇī vārtraghnī syādrohiṇyai hatveva śyetākṣyā āśāṃ neyāt

Let, then, the brown one, with red-brown eyes, be the Soma-cow. And if he be unable to obtain a brown one with red-brown eyes, let it be a dark-red one. And if he be unable to obtain a dark-red one, let it be a ruddy one, one of the Vritra-killer's own. But let him nowise turn his fancy upon a ruddy one with reddish-white eyes.