Sayyiduna Abu Hurayrah (may Allah be pleased with him) reported, concerning the Prophet's (peace and blessings be upon him) account of Makkah, that he (peace and blessings be upon him) said: "Its thorns are not to be uprooted, its trees are not to be cut, and its fallen items are not to be picked up, except by one who announces them."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب اللقطة / 12117