فَلَمَّا رَأَوْهُ عَارِضًا مُّسْتَقْبِلَ أَوْدِيَتِهِمْThen, when they saw it as a dense cloud approaching their valleys,meaning, when they saw the punishment coming towards them, they thought it to be clouds full of rain. That made them happy and joyful, because they had a drought and needed rain.قَالُوا هَذَا عَارِضٌ مُّمْطِرُنَاthey said:"This is a cloud bringing us rain!"Allah then said,بَلْ هُوَ مَا اسْتَعْجَلْتُم بِهِ رِيحٌ فِيهَا عَذَابٌ أَلِيمٌNay, but it is that which you were asking to be hastened -- a wind wherein is a painful torment!meaning, this is the torment that you called for saying, "Bring to us what you promise us if you should be of the truthful.