"Verily, this we have been promised -- we and our fathers before (us)! This is only the tales of the ancients!"
This means,
"It is impossible that we could be brought back. This was said by those who learned it from the books and disputes of the ancients."
This denial and rejection on their part is like the Ayah where Allah tells us about them:
أَءِذَا كُنَّا عِظَـماً نَّخِرَةً
قَالُواْ تِلْكَ إِذاً كَرَّةٌ خَـسِرَةٌ
فَإِنَّمَا هِىَ زَجْرَةٌ وَحِدَةٌ
فَإِذَا هُم بِالسَّاهِرَةِ
"Even after we are crumbled bones,"
They say: "It would in that case, be a return with loss!"
But it will be only a single Zajrah, When behold, they find themselves on the surface of the earth alive after their death. (79:11-14)
أَوَلَمْ يَرَ الاِنسَـنُ أَنَّا خَلَقْنَـهُ مِن نُّطْفَةٍ فَإِذَا هُوَ خَصِيمٌ مٌّبِينٌ
وَضَرَبَ لَنَا مَثَلً وَنَسِىَ خَلْقَهُ قَالَ مَن يُحىِ الْعِظَـمَ وَهِىَ رَمِيمٌ
قُلْ يُحْيِيهَا الَّذِى أَنشَأَهَأ أَوَّلَ مَرَّةٍ وَهُوَ بِكُلِّ خَلْقٍ عَلِيمٌ
Does not man see that We have created him from Nutfah. Yet behold he (stands forth) as an open opponent. And he puts forth for Us a parable, and forgets his own creation.
He says: "Who will give life to these bones after they are rotten and have become dust!"
Say: "He will give life to them Who created them for the first time! And He is the All-Knower of every creation!" (36:77-79)