Abu Wa'il Shaqiq bin Salamah (may Allah have mercy on him) said: Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) bought a slave girl from a man for six hundred, or nine hundred (dirhams). Then he searched for that seller for a year but did not find him. Then he took it (the money) out to the raised platform at the (mosque's) door and gave it in charity, a dirham and two dirhams at a time, on behalf of its owner. "Then, if its owner comes, he is to be given the choice: if he chooses the reward, it is his, and if he wants his wealth, he is to have his wealth." Sayyiduna Ibn Mas'ud (may Allah be pleased with him) said: "Do likewise with lost property (luqatah)." (These are the words of Abd al-Razzaq's narration.)
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9686