Mumonkan, Koan 15: Tozan's Sixty Blows

Zen Master Ummon

Tozan came to study with Ummon.
Ummon asked, "Where are you from?" 
"From Sato," Tozan replied.
"Where were you during the summer?" 
"Well, I was at the monastery of Hozu, south of the lake." 
"When did you leave there?" Ummon asked. 
"On August 25" was Tozan's reply. 
"I spare you sixty blows," Ummon said.

The next day Tozan came to Ummon and said, "Yesterday you said you spared me sixty blows. I beg to ask you, where was I at fault?" 
"Oh, you rice bag!" shouted Ummon.  "What makes you wander about, now west of the river, now south of the lake?" 

Tozan thereupon came to a mighty enlightenment experience.

Fundamentally speaking, Tozan never should have left Sato.  Seeking outside is wrong thinking. Sit in zazen anywhere. You have everything you need inside you, simply silence your thoughts.