Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.013A.

Dogs are considered impure. Any container that a dog has licked must be washed seven times, the first time with dirt. Abu Hurairah reported that the Messenger of Allah, upon whom be peace, said, “Purifying a container that a dog has licked is done by washing it seven times, the first washing being with dirt (that is, water mixed with dirt until it becomes muddy).” This was related by Muslim, Ahmad, Abu Dawud, and al-Baihaqi. If a dog licks a pot that has dry food in it, what it touched and what surrounds it must be thrown away. The remainder may be kept, as it is still pure. As for a dog’s fur, it is considered pure.