Narrated Ibn Abbas (Radi-Allahu 'anhu):

On the Day of the Conquest of Makkah, Allah's Apostle (Sallallahu 'Alaihi
Wa Sallam) said, "Allah has made this town a sanctuary. Its thorny bushes
should not be cut, its game should not be chased, and its fallen things
should not be picked up except by one who would announce it publicly."

Bukhari Vol. 2 : No. 657