Sayyidah Duba'ah bint al-Zubayr (may Allah be pleased with her) said: Sayyiduna al-Miqdad went to relieve himself and entered a ruin, and he saw a rat bringing out one dinar at a time from a hole, until it had brought out seventeen dinars. Then it brought out the edge of a green piece of cloth. Al-Miqdad (may Allah be pleased with him) said: I got up and pulled the edge of the cloth and found a dinar in it, so they became eighteen dinars. Al-Miqdad took them and asked permission to see the Prophet (peace and blessings be upon him). When he entered upon the Prophet (peace and blessings be upon him), he told him the whole story and said: "O Messenger of Allah, take its zakah." The Prophet (peace and blessings be upon him) said: "Did you extend your hand into the hole?" Al-Miqdad (may Allah be pleased with him) said: "No, by the One who sent you with the truth." Thereupon the Messenger of Allah (peace and blessings be upon him) said to al-Miqdad: "May Allah bless it for you."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17746