Shatapatha Brahmana 11.6.1.6

11.6.1.6

sa ha tata evodaṅ pravavrāja edu puruṣaiḥ puruṣānākrandayata ākrandayadbhiradyamānāntsa hovāca bhīṣmam bata bhoḥ puruṣānnvā etatpuruṣā ākrandayata ākrandayanto'dantīti te hocuritthaṃ vā ime'smānamu

He went forth from thence northward, and lo, men, crying aloud, were being eaten by men, crying aloud! He said, 'Horrible! woe is me! men, crying aloud, here are eating men, crying aloud!' 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.'