Narrated Ubai bin Ka'b, radiyAllâhu 'anhu: I found a purse containing one hundred Dinars. So I went to the Prophet, sallAllâhu 'alaihi wa salam (and informed him about it),

He, sallAllâhu 'alaihi wa salam said: "Make public announcement about it for one year"

I did so, but nobody turned up to claim it, so I again went to the Prophet, sallAllâhu 'alaihi wa salam, who said, "Make public announcement for another year."

I did, but none turned up to claim it. I went to him for the third time and he, sallAllâhu 'alaihi wa salam, said, "Keep the container and the string which is used for its tying and count the money it contains and if its owner comes, give it to him; otherwise, utilize it." 

The sub-narrator Salama said, "I met him (Suwaid, another sub-narrator) in Mecca and he said, 'I don't know whether Ubai made the announcement for three years or just one year.' " 

[Bukhari: Book 3 Vol 42 Hadith 608]