فَكَذَّبُوهُ فَعَقَرُوهَاThen they denied him and they killed it.which means they rejected what he came with. This resulted in them killing the she-camel that Allah had brought out of the rock as a sign for them and a proof against them.فَدَمْدَمَ عَلَيْهِمْ رَبُّهُم بِذَنبِهِمْSo their Lord destroyed them because of their sin,meaning, He became angry with them and He annihilated them.فَسَوَّاهَاFasawwaha!meaning, He made the punishment descend upon them all equally.Qatadah said,"It has reached us that the leader of tribe of Thamud did not kill the she-camel until their youth, their elderly, their males and their females all pledged allegiance to him. So when the people cooperated in killing her, Allah destroyed them all with the same punishment due to their sin."Allah said