Praise be to Allah.

Firstly: 

The scholars (may Allah have mercy on them) differed concerning the najaasah (impurity) of dogs and there are several opinions. 

It says in al-Mawsoo‘ah al-Fiqhiyyah (40/79): 

The fuqaha’ differed concerning dogs with regard to whether they are pure or impure. 

The Shaafa‘is and Hanbalis are of the view that dogs are impure in and of themselves. 

The Hanafis are of the view that dogs are not impure in and of themselves, rather their leftover (food or water) and wetness are impure.

The Maalikis are of the view that dogs are pure in and of themselves, because they say that the basic principle concerning all things is that they are pure, and all living beings, even dogs, are pure, and so are their sweat, tears, mucus and saliva. 

They also said: The fuqaha’ differed concerning the impurity of a vessel that has been licked by a dog. The majority of fuqaha’ are of the view that if a dog licks a vessel, it makes it impure. 

The Maalikis and some of the Hanafis are of the view that the licking of a dog does not make the vessel impure. End quote. 

Ibn ‘Abd al-Barr (may Allah have mercy on him) attributed the view that dogs are impure to the majority of the scholars among the Sahaabah and Taabi‘een. 

He said (may Allah have mercy on him): The scholars differed with regard to acting upon the apparent meaning of this hadeeth [about the licking of a dog, as we shall see below], and they also differed about what we shall mention, by Allah’s leave. Most of the scholars among the Sahaabah and Taabi‘een, and those who came after them of the fuqaha’ of the Muslims, said that a vessel should be washed seven times with water if it is licked by a dog.

End quote from at-Tamheed, 18/269 

He also said (may Allah have mercy on him): The fuqaha’ also differed concerning the leftover (food or water) of a dog or any water or food licked by a dog. The view of Maalik, which is the final view of his madhhab, is that the leftovers of a dog are taahir (pure) and a vessel licked by a dog should be washed seven times on the basis that it is mustahabb to do so, but not obligatory. 

Abu Haneefah and his companions, ath-Thawri and al-Layth ibn Sa‘d said that the leftovers of a dog are najis (impure), and they did not specify a number of times for washing (the vessel). They said: Rather he should wash it until he thinks it most likely that the impurity has been removed, whether that is one time or more. 

Al-Awzaa‘i said that the leftovers of the dog in the vessel are najis (impure), but in al-Mustaqni‘ it says that they are not impure. The garment should be washed if the dog’s saliva gets on it, and the meat of game (caught by the dog) should be washed to remove the dog’s saliva. 

Ash-Shaafa‘i, Ahmad ibn Hanbal, Ishaaq ibn Raahawayh, Abu ‘Ubayd, Abu Thawr and at-Tabari said: The leftovers of a dog are najis (impure) and the vessel should be washed seven times, the first of which should be with dust or soil. This is the view of the majority of the literalists. 

Dawood said: The leftovers of a dog are taahir (pure) and the vessel should be washed seven times, as an obligation, if the dog licked the vessel. Regardless of whether the vessel contained water or something other than water, it is taahir (pure), but one should wash the vessel seven times. However, one may do wudoo’ with the water that was licked, and the food and drink that were licked may be consumed. 

Abu ‘Umar said: Those (scholars) who were of the view that dogs are not najis (impure) say that their leftovers are taahir (pure) but the vessel should be washed seven times if the dog licked it. In their opinion this is so as to follow the instructions in the hadeeth to wash that which remains pure, and it is limited to this case. Those who are of the view that dogs are najis (impure) and that their leftovers are najis, and also said that the vessel must be washed seven times if the dog licks it, say that the hadeeth specifies seven times to purify this impurity, which is different from other types of impurity. 

Ash-Shaafa‘i and his companions said that dogs and pigs are najis (impure) whether alive or dead, and there is nothing among living beings that is najis apart from these two. He said: All parts of the dog (are impure), by analogy with its tongue…

End quote from at-Tamheed (18/269) 

The correct scholarly view is that all parts of the dog are najis, including its saliva and hair, because the Prophet (blessings and peace of Allah be upon him) said: “The way to purify the vessel of one of you, if a dog licks it, is to wash it seven times, the first of which should be with dust (or soil).” Narrated by Muslim. 

Al-Khattaabi (may Allah have mercy on him) said: What we learn from this hadeeth is that dogs are najis (impure) in and of themselves; if they were not najis, he would not have instructed us to purify the vessel if it is licked by a dog. Purification is basically prescribed to remove major or minor ritual impurity (ghusl and wudoo’) or wash off impure substances. The rulings on ritual impurity cannot apply to vessels, thus it is known that the aim here is to remove an impure substance. Once it is proven that the dog’s tongue, with which it drinks the water, is najis (impure) and it is obligatory to purify the water from that, it is known that all the parts (of the dog) are impure, like its tongue. So if any part of its body touches one, it must be purified. It also clearly shows that purification cannot be done with less than seven washings, and that rubbing it once with dust or soil is obligatory. 

It is obvious that the reason for using dust is to achieve a thorough purification. This highlights the high degree of the dog’s impurity. Therefore, other means of purification, such as potash and the like [used as cleansing substances], that are very effective in purification, may also be used in place of dust or soil.

End quote from Ma‘aalim as-Sunan (1/93) 

As-San‘aani (may Allah have mercy on him) said: This hadeeth points to several rulings: 

Firstly, the dog’s mouth is najis, because of the instruction to wash anything that the dog licks and pour away the water. He said “The purification of the vessel of one of you”, because there is no washing except in the case of ritual impurity or contamination with an impure substance. There is no ritual impurity in this case, therefore what is meant is contamination with an impure substance. Pouring it away is wasting the water; If the water was taahir (pure), he would not have instructed them to waste it, because he had forbidden them to waste water. This clearly indicates that the dog’s mouth is najis (impure), and the rest of the dog’s body is deemed to be the same, by analogy. That is because if it is proven that the dog’s saliva is najis, and its saliva is part of its mouth, as it is the sweat of its mouth, then its mouth is najis, because sweat is part of what comes from the body, so the rest of its body is the same… End quote from Subul as-Salaam (1/22). 

Based on that, if the dog puts its tongue or its foot or any other part of its body in the water, the water becomes najis (impure); hence the water must be poured away and the vessel must be washed. 

Thirdly: 

If the water that was licked by the dog spills onto your clothes or your body, and you are certain or think it most likely that it got onto your clothes or your body, then you have to wash the place affected by the impurity seven times, one of which should be with dust or soil, or whatever may take its place of cleansing substances such as soap, because dust may be harmful. But if you think it most likely that the water did not reach your clothes or your body, then you do not have to do anything, because the basic principle is that things are taahir (pure), but in this case there is some doubt concerning najaasah (impurity). 

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: 

With regard to lapping up (water), saliva comes out of the dog when it does this. If the dog’s saliva gets onto one’s clothes or anything else, then they should be washed seven times. But we do not say that one of them should be with dust or soil, because that might be harmful. Rather we say that instead of dust one should use soap or something similar to remove the impurity, and that, with the seven washings, is sufficient. 

End quote from Liqa’ al-Baab al-Maftooh, no. 49 

Note: it is not permissible to keep dogs except for a need such as guarding or hunting. If a person keeps a dog for any other purpose, he is sinning and every day one or two qiraats of hasanaat (good deeds) will be detracted from his reward. For more information, please see the answers to questions no. 69777 and 69840.

And Allah knows best.