Śatapatha Brāhmaṇa ("of a hundred paths") 11.6.1.4

11.6.1.4

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

He went forth from thence southward, and lo, men were dismembering men, cutting up their limbs one by one, and saying, 'This to thee, this to me!' He said, 'Horrible! woe is me! men here have dismembered men, cutting up 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.'