Śatapatha Brāhmaṇa ("of a hundred paths") 1.5.4.12

1.5.4.12

tasmātprathame prayāja iṣṭe brūyāt | eko mametyekā tasya yamahaṃ dveṣmīti yadyu na dviṣyādyo 'smāndveṣṭi yaṃ ca vayaṃ dviṣma iti brūyāt

For this reason let him (the sacrificer) say, when the first fore-offering has been performed, 'One (eka) for me!' and 'One (ekâ) for him whom we hate!' And if he should not hate any one, let him say, 'who hates us and whom we hate!'