Surah Al-Kahf (The Cave), Verse 22

سَیَقُوْلُوْنَ ثَلٰثَةٌ رَّابِعُهُمْ كَلْبُهُمْ وَیَقُوْلُوْنَ خَمْسَةٌ سَادِسُهُمْ كَلْبُهُمْ رَجْمًا بِالْغَیْبِ وَیَقُوْلُوْنَ سَبْعَةٌ وَّثَامِنُهُمْ كَلْبُهُمْ قُلْ رَّبِّیْۤ اَعْلَمُ بِعِدَّتِهِمْ مَّا یَعْلَمُهُمْ اِلَّا قَلِیْلٌ فَلَا تُمَارِ فِیْهِمْ اِلَّا مِرَآءً ظَاهِرًا وَّلَا تَسْتَفْتِ فِیْهِمْ مِّنْهُمْ اَحَدًا 

Sa yaqooloona salaasatur raabi'uhum kalbuhum wa yaqooloona khamsatun saadisuhum kalbuhum rajmam bilghaib; wa yaqooloona sab'atunw wa saaminuhum kalbuhum; qur Rabbeee a'lamu bi'iddatihim maa ya'lamuhum illaa qaleel; falaa tumaari feehim illaa miraaa'an zaahiranw wa laa tastafti feehim minhum ahadaa

“(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)." Enter not, therefore, into controversies concerning them, except on a matter that is clear, nor consult any of them about (the affair of) the Sleepers.”

Quran 18:22 (Yusuf Ali Translation)