Majma al-Zawaid — Hadith 6848

Sayyiduna Ya'la bin Murrah (may Allah be pleased with him) reports this saying of the Prophet (peace and blessings be upon him): "Whoever finds a minor lost item, such as a garment or something similar, must announce it for three days; and whoever finds a lost item of greater value than that must announce it for six days. If its owner comes, well and good; otherwise, he must give it in charity. Then, if its owner comes, he must give him the choice."
Al-Tabarani recorded it in al-Mu'jam al-Kabir; its chain contains a narrator, Umar bin Abdullah bin Ya'la, who is da'if (weak).