لَوْ يَعْلَمُ الَّذِيْنَ كَفَرُوْا حِيْنَ لَا يَكُفُّوْنَ عَنْ وُّجُوْهِهِمُ النَّارَ وَلَا عَنْ ظُهُوْرِهِمْ وَلَا هُمْ يُنْصَرُوْنَ ( الأنبياء: ٣٩ )
Law ya'lamul lazeena kafaroo heena laa yakuffoona 'anw wujoohihimun Naara wa laa 'an zuhoorihim wa laa hum yunsaroon (al-ʾAnbiyāʾ 21:39)
If those who disbelieved but knew the time when they will not avert the Fire from their faces or from their backs and they will not be aided... (Al-Anbya  : 39)
1 Mufti Taqi Usmani
Only if the disbelievers were to know the time when they will not (be able to) keep off the fire from their faces or from their backs, nor will they be helped.