The Tipiṭaka in Three Languages

Khuddakavatthukkhandhaka

Vinayapiṭaka · Cūḷavagga (2) · Vol. 7 · Section 178

[178] Now at that time the group-of-six bhikkhus (chabbaggiyā bhikkhū) climbed trees and moved from tree to tree. People complained, criticized, and spread it about, … "just like monkeys" … They reported this matter to the Blessed One. … "Bhikkhus, a tree should not be climbed. Whoever should climb one commits an offense of wrong-doing (dukkaṭa)."

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.

This passage also appears in 2 other places