YV 4.6j

' Therefore it is drawn for Mitra and Varuna together; therefore with a king as helper they slay a king, with a Vaiçya a Vaiçya, with a Çudra a Çudra. This was not day or night, but undiscriminated; the gods said to Mitra and Varuna, 'Make this to shine forth for us'; they replied, 'Let us choose a boon; let one cup only be drawn before ours.' Therefore the cup for Indra and Vayu is drawn before that for Mitra and Varuna, for the Upançu and the Antaryama (cups) are expiration and inspiration. Mitra produced the day, Varuna the night; then indeed did this shine forth; in that (a cup) is drawn for Mitra and Varuna, (it is) for shining forth. The head of the sacrifice was cut; the gods said to the Açvins, Ye are physicians; do ye replace the head of the sacrifice', they replied. Let us choose a boon; let there be drawn a cup for us also herein.' For them they drew this cup for the Açvins; then indeed did they replace the head of the sacrifice; in that (the cup) for the Açvins is drawn, (it is) to restore the sacrifice. The gods said of these two, 'Impure are they, wandering among men [1] and physicians.' Therefore a Brahman should not practise medicine, for the physician is impure, unfit for the sacrifice. Having purified them by the Bahispavamana (Stotra) they drew for them this cup for the Açvins; therefore (the cup) for the Açvins is drawn when the Bahispavamana has been sung. Therefore by one who knows thus the Bahispavamana should be performed; verily he purifies himself. Their skill as physicians they deposited in three places, in Agni a third, in the waters a third, in the Brahman a third. Therefore one should put beside him a pot of water [2] and sit on the right hand of a Brahman when practising medicine; all medicine he performs thereby, his remedy becomes effective. The theologians say, 'For what reason are cups for two deities drawn in one vessel, but offered in two?