ٱلْوَاقِعَة : ٦

  • فَكَانَتۡ So they become
  • هَبَآءٗ dust particles
  • مُّنۢبَثّٗا dispersing
And become dust dispersing,
so that they become a scattered dust (the second idh, 'when', is a substitution for the first idh),