Musnad Ahmad 26:66

Abu Mu'awiyah narrated to us, al-A'mash narrated to us, from Muslim, from Masruq, who said: A man came to Abdullah and said: "I left a man in the mosque interpreting the Quran according to his own opinion. He says regarding this verse: {The day the sky will bring a visible smoke} [Ad-Dukhan: 10] until the end of it: 'A smoke will cover them on the Day of Resurrection, seizing their breaths until it afflicts them like the state of a cold.'" Abdullah said: "Whoever possesses knowledge, let him speak with it, and whoever does not know, let him say: 'Allah knows best.' For it is part of a man's understanding to say regarding what he does not know: 'Allah knows best.' This was only because when the Quraysh defied the Prophet, may Allah bless him and grant him peace, he invoked [Allah] against them with years like the years of Yusuf. They were struck by drought and hardship until they ate bones. A man would look toward the sky and see between himself and the sky something like the appearance of smoke due to the hardship. So Allah, the Mighty and Majestic, revealed: {So watch for the day when the sky will bring a visible smoke. Covering the people; this is a painful torment} [Ad-Dukhan: 10-11]. Then the Messenger of Allah, may Allah bless him and grant him peace, was approached and it was said: 'O Messenger of Allah, ask Allah for rain for Mudar, for they have perished.' He prayed for them, and Allah, the Mighty and Majestic, revealed: {Indeed, We will remove the torment} [Ad-Dukhan: 15]. But when the second time struck them, they returned [to disbelief], so it was revealed: {The day We will strike with the greatest assault; indeed, We will take retribution} [Ad-Dukhan: 16]—the day of Badr."