Śatapatha Brāhmaṇa ("of a hundred paths") 3.9.4.1

3.9.4.1

athādhiṣavaṇe paryupaviśanti | athāsyāṃ hiraṇyam badhnīte dvayaṃ vā idaṃ na tṛtīyamasti satyaṃ caivānṛtaṃ ca satyameva devā anṛtam manuṣyā agniretasaṃ vai hiraṇyaṃ satyenāṃśūnupaspṛśāni satyena somam parāhaṇānīti tasmādvā asyāṃ hiraṇyam badhnīte

Thereupon they sit down round the two press-boards. He (the Adhvaryu) then ties a piece of gold to that (nameless finger). For twofold, verily, is this; there is no third, namely, the truth and the untruth; the gods, forsooth, are the truth, and men are the untruth. And the gold has sprung from Agni's seed: 'With the truth I will touch the stalks, with the truth I will take hold of Soma,' thus he thinks, and therefore he ties a piece of gold to that (ring-finger).