Gaddulabaddhasutta 2.1

2.1

Seyyathāpi, bhikkhave, sā gaddulabaddho daḷhe khīle vā thambhe vā upanibaddho tameva khīlaṃ vā thambhaṃ vā anuparidhāvati anuparivattati;

Suppose a hound on a leash was tethered to a strong post or pillar. It would just keep running and circling around that post or pillar.