Śatapatha Brāhmaṇa ("of a hundred paths") 11.6.1.5

11.6.1.5

sa ha tata eva pratyaṅ pravavrāja edu puruṣaiḥ puruṣāṃstūṣṇīmāsīnāṃstūṣṇīmāsīnairadyamānāntsa hovāca bhīṣmam bata bhoḥ puruṣānnvā etatpuruṣāstūṣṇīmāsīnāṃstūṣṇīmāsīnā adantīti te hocuritthaṃ vā ime'smānamuṣmiṃloke'sacanta tānvayamidamiha pratisacāmahā iti sa hovācāstīha prāyaścittī3rityastīti kā-ti pitaiva te vedeti

He went forth from thence westward, and lo, men, sitting still, were being eaten by men, sitting still! He said, 'Horrible! woe is me! men, sitting still, are eating men, sitting still!' They replied, 'Thus, indeed, these have 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.'