It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "Its grass is not to be cut, its trees are not to be cut, its game is not to be chased away, and picking up its lost property is not lawful except for one who announces it." Sayyiduna Abbas (may Allah be pleased with him) said: O Messenger of Allah! Except idhkhir. He (peace and blessings be upon him) said: "Idhkhir is permitted."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب اللقطة / 12119