Sunan Ibn Majah — The Chapters on Lost Property — Hadith No: 2506
Translation
It was narrated that Suwaid bin Ghafalah said:“I went out with Zaid bin Suhan and Salman bin Rabi'ah, and when we were at `Udhaib, I found a whip. They said to me: 'Throw it away,' but I refused. When we came to Al-Madinah I went to Ubayy bin Ka'b and told him about that. He said: 'You did the right thing. I found one hundred dinar that had been lost at the time of the Messenger of Allah (ﷺ), and I asked him about it. He said, “Announce it for a year.” So I Announced it, and I did not find anyone who recognized it. He said: “Remember the features of its bag and strap, and how many it contains, then announce it for a year. If someone comes who describes it with those features, (give it to him), otherwise it is like your own property.”