Śatapatha Brāhmaṇa ("of a hundred paths") 11.6.1.3

11.6.1.3

sa ha tata eva prāṅ pravavrāja edu puruṣaiḥ puruṣānparvāṇyeṣām parvaśaḥ saṃvraścam parvaśo vibhajamānānidaṃ tavedam mameti sa hovāca bhīṣmam bata bhoḥ puruṣānnvā etatpuruṣāḥ parvāṇyeṣāṃ saṃvraścam parvaśo vyabhakṣateti te hocuritthaṃ vā ime'smānamuṣmiṃloke'sacanta tānvayamidamiha pratisacāmahā iti sa hovācāstīha prāyaścittī3rityastīti kā-ti pitā te vedeti

He then went forth from thence eastward, and lo, men were dismembering men, hewing off their limbs one by one, and saying, 'This to thee, this to me!' He said, 'Horrible! woe is me! men here have dismembered men, hewing off their limbs one by one!' They replied, 'Thus, indeed, these dealt with us in yonder world, and so we now deal with them in return.' He said, 'Is there no atonement for this?'--'Yes, there is,' they replied.--'What is it?'--'Thy father knows.'