The Prophet (blessings and peace of Allah be upon him) was keen to explain issues pertaining to purification, and to explain to them which substances were impure, and how to remove their traces and purify an item that had been contaminated with them. An example of that is what is mentioned in this hadith, in which the Prophet (blessings and peace of Allah be upon him) enjoined washing a vessel seven times if a dog drinks from it. The procedure that is sufficient to purify the vessel from which a dog has drunk is to wash it seven times, one of which should be with dust or soil, as was narrated by al-Nasa’i: “… one of which should be with dust.” According to a report narrated by Muslim, “The first of which should be with dust”; according to another report narrated by Muslim, “and the eighth time rub it with dust.” The dog is singled out for mention in this regard, because of what is known about how impure (najis) the dog is, and how it may carry many diseases in its saliva. There is wisdom behind cleaning the vessel this number of times in this manner, which is known to Allah (may He be glorified and exalted). It was said that using dust or soil to wash the vessel is to be done because dust or soil has the ability to kill the diseases that are usually caused by the dog and may attach themselves to the vessel, which water alone cannot remove. Repeatedly washing the vessel with water will ensure that it is clean. There is no difference between different types of dogs in this regard, and whether they are the types of dogs that it is permissible to keep, such as hunting dogs, or they are types that it is not permissible to keep..