Sahih Bukhari Volume 6, Book 60, Hadith Number 333.

Narrated By Masruq : We came upon ‘Abdullah bin Mas’ud and he said “O people! If somebody knows something, he can say it, but if he does not know it, he should say, “Allah knows better,’ for it is a sign of having knowledge to say about something which one does not know, ‘Allah knows better.’ Allah said to His Prophet: ‘Say (O Muhammad!) No wage do I ask of You for this (Quran) nor am I one of the pretenders (a person who pretends things which do not exist).’ (38.86) Now I will tell you about Ad-Dukhan (the smoke), Allah’s Apostle invited the Quraish to embrace Islam, but they delayed their response. So he said, “O Allah! Help me against them by sending on them seven years of famine similar to the seven years of famine of Joseph.” So the famine year overtook them and everything was destroyed till they ate dead animals and skins. People started imagining to see smoke between them and the sky because of severe hunger. Allah said:

‘Then watch you for the Day that the sky will bring forth a kind of smoke plainly visible, covering the people… This is painful torment.’ (44.10-11) (So they invoked Allah) “Our Lord! Remove the punishment from us really we are believers.” How can there be an (effectual) reminder for them when an Apostle, explaining things clearly, has already come to them? Then they had turned away from him and said: ‘One taught (by a human being), a madman?’ ‘We shall indeed remove punishment for a while, but truly, you will revert (to disbelief).’ (44.12-15) Will the punishment be removed on the Day of Resurrection?” ‘Abdullah added, “The punishment was removed from them for a while but they reverted to disbelief, so Allah destroyed them on the Day of Badr. Allah said:

‘The day We shall seize you with a mighty grasp. We will indeed (then) exact retribution.'” (44.16)