Allah said that they ask you to inform them (saying):

أَحَقٌّ هُوَ

("Is it true") asking about the return and the Resurrection from the graves, after the bodies become sand.

قُلْ إِى وَرَبِّى إِنَّهُ لَحَقٌّ وَمَآ أَنتُمْ بِمُعْجِزِينَ

(Say: "Yes! By my Lord! It is the very truth! And you cannot escape it!") meaning that becoming sand does not make Allah incapable of bringing you back, since He originated you from nothing.

إِنَّمَآ أَمْرُهُ إِذَآ أَرَادَ شَيْئاً أَن يَقُولَ لَهُ كُن فَيَكُونُ

(Verily, His command, when He intends a thing, is only that He says to it, `Be!' - and it is!)36:82 There are only two other Ayat in the Qur'an similar to this. Allah commands His Messenger to give an oath by Him to answer those who deny the return. He said in Surah Saba',

وَقَالَ الَّذِينَ كَفَرُواْ لاَ تَأْتِينَا السَّاعَةُ قُلْ بَلَى وَرَبِّى لَتَأْتِيَنَّكُمْ

(Those who disbelieve say: "The Hour will not come to us." Say: "Yes, by my Lord!, it will come to you.") (34:3) The second is in Surat At-Taghabun, He said:

زَعَمَ الَّذِينَ كَفَرُواْ أَن لَّن يُبْعَثُواْ قُلْ بَلَى وَرَبِّى لَتُبْعَثُنَّ ثُمَّ لَتُنَبَّؤُنَّ بِمَا عَمِلْتُمْ وَذَلِكَ عَلَى اللَّهِ يَسِيرٌ

(The disbelievers claimed that they will never be resurrected. Say: "Yes! By my Lord! you will certainly be resurrected, then you will be informed of (and recompensed for) what you did; and that is easy for Allah.") (64:7) Then Allah informed us that when the Resurrection is established the disbelievers will wish that they could ransom themselves from Allah's punishment with the equivalent of the weight of the earth in gold.

وَأَسَرُّواْ النَّدَامَةَ لَمَّا رَأَوُاْ الْعَذَابَ وَقُضِىَ بَيْنَهُمْ بِالْقِسْطِ وَهُمْ لاَ يُظْلَمُونَ

(And they would feel in their hearts regret when they see the torment, and they will be judged with justice, and no wrong will be done unto them.)