Musannaf Ibn Abi Shaybah

Hazrat Thumamah bin Abdullah bin Anas narrates from his grandfather Hazrat Anas that he was asked about a mouse falling into clarified butter or olive oil. He replied: If the clarified butter is solid, then the mouse and the surrounding butter should be taken out, and the rest may be eaten. But if the butter is melted, then it should be used for lighting lamps.