سيقولون ثلاثة رابعهم كلبهم ويقولون خمسة سادسهم كلبهم رجما بالغيب ويقولون سبعة (18:22) بالانجليزي

(18:22) Some people will say, "They were three and the fourth was their dog", and some others will say, "They were five and the sixth was their dog." These are mere irrelevant guesses. There are still others who say, "They were seven and the eighth was their dog. " *22 Say, "My Lord alone knows best how many they were." "There are a few people only who know their correct number: so you should not enter into discussions with them about their number except in a cursory way: nor ask anyone about them *23

Tafseer Abu-al-A'la Maududi

Page 296 English Traditional

*22) This shows that about three hundred years after this event, at the time of the revelation of the Qur'an, different stories had become current among the Christians about the Sleepers of the Cave, but generally these stories had no authentic source behind them.' This was because that was not the age of the press in which authentic books might have been published. Therefore naturally the stories of events were carried from place to place by means of oral traditions, and with the passage of time many tales of fiction got mixed up with the real story.
*23) This is meant to impress that the real thing in this story is not the number of the Sleepers but the lessons it teaches: (1) A true believer should not on any account turn away from the truth and bow before falsehood. (2) A believer should not merely rely on the material means but on AIIah. He should trust in God and follow the right way, even though the outward adverse circumstances might appear to be unfavourable. (3) It is wrong to suppose that Allah is bound by any so-called "Law of Nature", for He is able to do any thing He wills even though that might seem to be against some common experience. He has the power to change any so-called law of nature, whenever and wherever He wills and bring about any extraordinary "supernatural" thing. So much so that He can raise up anyone who might have been asleep for two hundred years, as if he had slept only for a few hours, without letting any change take place in his appearance, dress, health, indeed in anything, during the passage of time. (4) This teaches us that Allah has the power to bring to life all the generations-past, present and futureall together as asserted by the Prophets and Divine Scriptures. (5) It teaches us that ignorant people have always been perverting the Signs of Allah which are sent for the right guidance of the people. That is how the miracle of the Sleepers of the Cave, which had been shown as a proof of the Hereafter, had been turned into a means of shirk, as if they were some saints who had been sent only for this purpose.
It is obvious from the above-mentioned real lessons, which one can learn from the story of the Sleepers, that a wise man will pay his attention to these things and not divert it in search of their number, their names, the colour of their dog and the like. Only those people, who have no interest for the reality but for superficial things, will spend their time and energy in making investigations about such things. That is why AIIah instructed the Holy Prophet: "You should not enter into useless and irrelevant discussions about such things, if other people try to involve you in them. Instead of wasting your time in such useless things, you should concentrate your attention only on your mission." That is why Allah has not Himself told their exact number lest it should encourage such people as are always hankering after useless things.