Lokantagamana Sutta
At Sāvatthi.
“Monks, the end of the world cannot be known, seen, or reached by travelling. However, without knowing the end of the world there is no end of suffering.” Having taught the Dhamma in brief, the Blessed One entered his dwelling.
The monks, therefore, approached Ānanda and asked him to explain in detail what the Blessed One had taught in brief.
Ānanda explains that the six senses, by which the world is perceived and conceived are “the world” in the Noble One’s discipline.
The monks relate what Ānanda taught to the Blessed One, who praises Ānanda’s wisdom. S.iv.93.