It was narrated from Abu Hurairah that :
the Messenger of Allah ﷺ said to a man: "What do you say during your prayer?" He said: "I recite the Tashah-hud then I ask for Allah for Paradise and see refuge with Him from Hell, but by Allah I do not understand your whispering or the whispering of Mu'adh." He said: "It is concerning them (Paradise and Hell) that we are whispering."

حَدَّثَنَا يُوسُفُ بْنُ مُوسَى الْقَطَّانُ، حَدَّثَنَا جَرِيرٌ، عَنِ الأَعْمَشِ، عَنْ أَبِي صَالِحٍ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ ﷺ لِرَجُلٍ " مَا تَقُولُ فِي الصَّلاَةِ " . قَالَ أَتَشَهَّدُ ثُمَّ أَسْأَلُ اللَّهَ الْجَنَّةَ وَأَعُوذُ بِهِ مِنَ النَّارِ أَمَا وَاللَّهِ مَا أُحْسِنُ دَنْدَنَتَكَ وَلاَ دَنْدَنَةَ مُعَاذٍ . قَالَ " حَوْلَهُمَا نُدَنْدِنُ " .