Musnad Ahmad 1163:8

Muhammad ibn Mus'ab narrated to us, he said: Al-Awza'i narrated to us, from Al-Zuhri, from 'Ubayd Allah ibn 'Abd Allah, from Ibn 'Abbas, from Maymunah, the wife of the Prophet, may God bless him and grant him peace: That she asked the Messenger of God, may God bless him and grant him peace, for a legal opinion regarding a mouse that fell into some ghee of theirs that was solid. He said: "Throw it away and what is around it, and eat your ghee."