Or [any] creation of that which is great within your breasts." And (17:51)

﴿أَوْ خَلْقًا مِّمَّا يَكْبُرُ فِي صُدُورِكُمْ ۚ فَسَيَقُولُونَ مَن يُعِيدُنَا ۖ قُلِ الَّذِي فَطَرَكُمْ أَوَّلَ مَرَّةٍ ۚ فَسَيُنْغِضُونَ إِلَيْكَ رُءُوسَهُمْ وَيَقُولُونَ مَتَىٰ هُوَ ۖ قُلْ عَسَىٰ أَن يَكُونَ قَرِيبًا﴾
[ الإسراء: 51]

17:51 Or [any] creation of that which is great within your breasts." And they will say, "Who will restore us?" Say, "He who brought you forth the first time." Then they will nod their heads toward you and say, "When is that?" Say, "Perhaps it will be soon -

Or become some other creation greater than them amongst that which is considered great in your hearts.
Allah shall restore you just as He initiated you and He shall bring you back to life just as He created you in the first instance.
These opponents will say: Who will bring us back to life after we die? Say to them: He who created you in the first instance without any precedent shall restore you.
Then they will shake their heads, mocking your response to them, and say unbelievingly: When will this restoration be? Say to them: Perhaps it is near, as everything which is coming will soon arrive.

"Or some created thing that is yet greater (or harder) in your breasts (thoughts to be resurrected, even then you shall be resurrected)" Then, they will say: "Who shall bring us back (to life)?" Say: "He Who created you first!" Then, they will shake their heads at you and say: "When will that be?" Say: "Perhaps it is near!"

phonetic Transliteration

Aw khalqan mimma yakburu fee sudoorikum fasayaqooloona man yuAAeeduna quli allathee fatarakum awwala marratin fasayunghidoona ilayka ruoosahum wayaqooloona mata huwa qul AAasa an yakoona qareeban

Abdullah Yusuf Ali - Translation

"Or created matter which, in your minds, is hardest (to be raised up),- (Yet shall ye be raised up)!" then will they say: "Who will cause us to return?" Say: "He who created you first!" Then will they wag their heads towards thee, and say, "When will that be?" Say, "May be it will be quite soon!

Safi-ur-Rahman al-Mubarakpuri

"Or some created thing that is yet greater (or harder) in your breasts." Then, they will say: "Who shall bring us back (to life)" Say: "He Who created you first!" Then, they will shake their heads at you and say: "When will that be" Say: "Perhaps it is near!"

Page 287 English transliteration