Maliks Muwatta Book 36, Hadith Number 47.
Section : The Judgement on Lost Property.
Malik related to me from Ayyub ibn Musa from Muawiya ibn Abdullah ibn Badr al-Juhani that his father informed him that he stopped with a people on the way to Syria and he found a purse which had eighty dinars in it. He mentioned that to Umar ibn al-Khattab. Umar said to him, “Announce it at the doors of the mosques and mention it to everyone who comes from Syria for a year. When a year passes, it is your business.”