Musnad Ahmad 30:2356

Abu Mu'awiyah narrated to us, he said: Al-A'mash narrated to us, from Abu Razin, from Abu Hurairah, who said: I saw him striking his forehead with his hand, and he said: "O people of Iraq, you claim that I lie about the Messenger of Allah, may Allah bless him and grant him peace. May the benefit be yours, and the sin be upon me. I bear witness that I heard the Messenger of Allah, may Allah bless him and grant him peace, say: 'If the sandal strap of one of you breaks, let him not walk in the other until he repairs it.' 'And if a dog laps from the vessel of one of you, let him not perform ablution until he washes it seven times.'"