Pathikasutta 1.7.3

1.7.3

Tena kho pana samayena acelo korakkhattiyo kukkuravatiko catukkuṇḍiko chamānikiṇṇaṃ bhakkhasaṃ mukheneva khādati, mukheneva bhuñjati.

Now at that time a naked ascetic who was an aristocrat of Kuru had taken a vow to behave like a dog. When food is tossed on the ground, he gets down on all fours, eating and devouring it just with his mouth.