Sunan Ibn Majah Book 18, Hadith 7

That he went out one day to Al-Baqi', which is the graveyard, to relieve himself. People used to go out to relieve themselves only every two or three days, and their faces was like that of a camel (because of hunger and rough food). Then he entered a ruin and while he was squatting to relieve himself, he saw a rat bringing a Dinar out of a hole, then it went in and brought out another, until it had brought out seventeen Dinars. Then it brought out a piece of red rag.Miqdad said: “I picked up the rag and found another Dinar inside it, thus completing eighteen Dinar. I took them out and brought them to the Messenger of Allah (ﷺ), and told him what had happened. I said, 'Take its Sadaqah (charity), O Messenger of Allah (ﷺ).' He said: 'Take them back, for no Sadaqah is due on them. May Allah (SWT) bless them for you.' Then he said: 'Perhaps you put your hand in the hole?' I said: 'No, by the One Who has honored you with the truth.”