Is it a condition for purifying the impurity of a dog to wash with earth, or can alternatives like soap be used?

The impurity of a dog must be washed seven times, one of them with earth (soil). The Shafi'is hold that nothing other than earth suffices, while the Hanbalis permit the use of other cleansing agents. Sheikh Ibn 'Uthaymin preferred the obligation of using earth due to the specific textual evidence for it and its benefit in killing germs.