What does the Quran say about dogs?

 Quran talks about dogs in 2 places. If we summarize:

DOGS ARE FRIEND OF HUMAN:

In Quran chapter 18, the story of a group of youths is described, who hid inside a cave to escape a religious persecution. God made them fall in sleep and they had woken up some 300 years later. When the people of the cave were sleeping, their dog accompanied them. There is disagreement about how many people were there, but there is no disagreement that Dog was there.

“Some) say they were three, the dog being the fourth among them; (others) say they were five, the dog being the sixth,- doubtfully guessing at the unknown; (yet others) say they were seven, the dog being the eighth. Say thou: "My Lord knoweth best their number; it is but few that know their (real case).” (Quran 18:22)

Chapter 18 is one of the mysterious chapters of Quran which is full of parable to teach wisdom. Some may say that mention of Dog in this story is just a random thing. But God mentions nothing without purpose. He wanted to show his preference of Dog as faithful companion of human and their beneficiary nature. In fact, in the very same chapter God said:

“We have mentioned in this Qur'an all kind of examples for the benefit of people, but, more than anything else, man is argumentative! (Quran 18:54)

ALLAH DOESN’T ABANDON PEOPLE WHEN DOG IS PRESENT:

They were being taken care off by turning their sides continuously to prevent bed sores.

“Thou wouldst have deemed them awake, whilst they were asleep, and WE turned them on their right and on their left sides: their dog stretching forth his two fore-legs on the threshold: (Quran 18:18 part)

There was something else to take care of them (to turn their side) and people could be afraid of seeing them. According to one opinion, when Allah use the word “we”, it means angels are involved in the action.

 “if thou hadst come up on to them, thou wouldst have certainly turned back from them in flight, and wouldst certainly have been filled with terror of them.” (Quran 18:18, part)

SALIVA OF DOG DOESN’T MAKE A FOOD IMPURE TO EAT:

You can eat food seized by dog simply by slaughtering it in Islamic way.

“They ask you what (is) made lawful for them. Say, "Are made lawful for you the good things and what you have taught (your) hunting animals, ones who train animals to hunt you teach them of what Allah has taught you. So eat of what they catch for you, but mention (the) name (of) Allah on it” (Quran 5:4, literal word to word translation)

Dog is not mentioned in any other places (in 7:176 a parable is mentioned).

THAT IS ALL QURAN SAYS ABOUT DOG!

Disclaimer: Quran-centric opinion