It (i.e., the imagined smoke) was because, when the Quraish refused to obey the Prophet, he asked Allah to afflict them with years of famine similar to those of (Prophet) Joseph. So they were stricken with famine and fatigue, so much so that they ate even bones. A man would look towards the sky and imagine seeing something like smoke between him and the sky because of extreme fatigue. So Allah revealed:-- 'Then watch you for the Day that the sky will bring forth a kind of smoke plainly visible, covering the people; this is a painfull of torment.' (44.10-11) Then someone (Abu Sufyan) came to Messenger of Allah ﷺ and said, "O Messenger of Allah ﷺ! Invoke Allah to send rain for the tribes of Mudar for they are on the verge of destruction." On that the Prophet ﷺ said (astonishingly) "Shall I invoke Allah) for the tribes of Mudar? Verily, you are a brave man!" But the Prophet prayed for rain and it rained for them. Then the Verse was revealed. 'But truly you will return (to disbelief).' (44.15) (When the famine was over and) they restored prosperity and welfare, they reverted to their ways (of heathenism) whereupon Allah revealed: 'On the Day when We shall seize you with a Mighty Grasp. We will indeed (then) exact retribution.' (44.16) The narrator said, "That was the day of the Battle of Badr." (Using translation from Bukhārī 4821)   

عَبْدُ اللهِ إِنَّ قُرَيْشًا لَمَّا اسْتَعْصَتْ عَلَى رَسُولِ اللهِ ﷺ دَعَا عَلَيْهِمْ بِسِنِينَ كَسِنِي يُوسُفَ فَأَصَابَهُمْ قَحْطٌ وَجَهْدٌ حَتَّى أَكَلُوا الْعِظَامَ وَجَعَلَ يَعْنِي الرَّجُلَ يَنْظُرُ إِلَى السَّمَاءِ فَيَرَى بَيْنَهُ وَبَيْنَهَا كَهَيْئَةِ الدُّخَانِ مِنَ الْجَهْدِ فَأَنْزَلَ اللهُ ﷻ {يَوْمَ تَأْتِي السَّمَاءُ بِدُخَانٍ مُبِينٍ يَغْشَى النَّاسَ هَذَا عَذَابٌ أَلِيمٌ} [الدخان 11] فَأُتِيَ رَسُولُ اللهِ فَقِيلَ يَا رَسُولَ اللهِ اسْتَسْقِ اللهَ لَهُمْ فَإِنَّهُمْ قَدْ هَلَكُوا فَاسْتَسْقَى اللهَ فَسُقُوا فَأَنْزَلَ اللهُ تَعَالَى {إِنَّا كَاشِفُو الْعَذَابِ قَلِيلًا إِنَّكُمْ عَائِدُونَ} [الدخان 15] فَعَادُوا إِلَى حَالَتِهِمُ الَّتِي كَانُوا عَلَيْهَا حِينَ أَصَابَتْهُمُ الرَّفَاهِيَةُ فَأَنْزَلَ اللهُ تَعَالَى {يَوْمَ نَبْطِشُ الْبَطْشَةَ الْكُبْرَى إِنَّا مُنْتَقِمُونَ} [الدخان 16] قَالَ يَوْمَ بَدْرٍ  

"The Messenger of Allah ﷺ looked out from a room, when we were talking about the Hour. He said: 'The Hour will not begin until ten signs appear: The rising of the sun from the west (place of its setting); Dajjal; the smoke; the beast; Gog and Magog people; the appearance of 'Eisa bin Maryam(as), the earth collapsing three times - once in the east, one in the west and one in the Arabian Peninsula; and fire that will emerge from the plain of Aden Abyan and will drive the people to the place of Gathering, stopping with them when they stop at night and when they stop to rest at midday." (Using translation from Ibn Mājah 4055)   

اطَّلَعَنَا رَسُولُ اللهِ ﷺ وَنَحْنُ نَتَذَاكَرُ السَّاعَةَ فَقَالَ إِنَّ السَّاعَةَ لَا تَقُومُ حَتَّى تَكُونَ عَشْرٌ الدُّخَانُ وَالدَّجَّالُ وَطُلُوعُ الشَّمْسِ مِنْ مَغْرِبِهَا وَالدَّابَّةُ وَثَلَاثَةُ خُسُوفٍ خَسْفٌ بِالْمَشْرِقِ وَخَسْفٌ بِالْمَغْرِبِ وَخَسْفٌ فِي جَزِيرَةِ الْعَرَبِ وَنُزُولُ عِيسَى ابْنِ مَرْيَمَ وَفَتْحُ يَأْجُوجَ وَمَأْجُوجَ وَنَارٌ تَخْرُجُ مِنْ قَعْرِ عَدَنٍ تَسُوقُ النَّاسَ إِلَى الْمَحْشَرِ  

[Machine] Indeed, when the Quraysh became stubborn against the Messenger of Allah ﷺ, he said, "O Allah, assist me with seven like the aid of Prophet Yusuf." So, they were afflicted with a year of famine during which everything was rationed, and they had to eat the hides and carrion. Another narration says they had to eat the hides and bones. Then, the famine became so severe that it seemed like smoke rising from the ground. Abu Sufyan came and said, "Indeed, your people have been destroyed, so pray to Allah for them." He responded, "If they repent, we will count their number." This is in reference to the verse, {The Day the heaven will bring forth a visible smoke, covering the people, this is a painful torment} [Ad-Dukhan 11]. Abdullah asked, "Will the punishment of the Hereafter be revealed?" Then, Abdullah said, "Indeed, the smoke has passed."  

إِنَّ رَسُولَ اللهِ ﷺ لَمَّا اسْتَعْصَتْ عَلَيْهِ قُرَيْشٌ قَالَ «اللهُمَّ أَعِنِّي بِسَبْعٍ كَسَبْعِ يُوسُفَ» فَأَخَذَتْهُمْ سَنَةٌ فَحَصَتْ كُلَّ شَيْءٍ فَأَكَلُوا الْجُلُودَ وَالْمَيْتَةَ وَقَالَ الْآخَرُ الْجُلُودَ وَالْعَظْمَ فَجَعَلَ يَخْرُجُ مِنَ الْأَرْضِ كَهَيْئَةِ الدُّخَانِ فَجَاءَ أَبُو سُفْيَانَ فَقَالَ إِنَّ قَوْمَكَ قَدْ هَلَكُوا فَادْعُ اللهَ لَهُمْ فَقَالَ «إِنْ تَعُودُوا نَعُدْ» فَذَلِكَ قَوْلُهُ {يَوْمَ تَأْتِي السَّمَاءُ بِدُخَانٍ مُبِينٍ يَغْشَى النَّاسَ هَذَا عَذَابٌ أَلِيمٌ} [الدخان 11] قَالَ عَبْدُ اللهِ فَهَلْ يُكْشَفُ عَذَابُ الْآخِرَةِ؟ ثُمَّ قَالَ عَبْدُ اللهِ إِنَّ الدُّخَانَ قَدْ مَضَى  

[Machine] And Abu Jahl said, "Does Muhammad frighten us with the tree of Zaqqum? Bring dates and froth so that we may retaliate."  

وَقَالَ أَبُو جَهْلٍ أَيُخَوِّفُنَا مُحَمَّدٌ بِشَجَرَةِ الزَّقُّومِ هَاتُوا تَمْرًا وَزُبْدًا فَتَزَقَّمُوا