Sunan Ibn Majah
3847
Sahih+3

It was narrated from Abu Hurairah that :the Messenger of Allah (saas) 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

SahihAl-Albani
SahihMuhammad Fouad Abd al-Baqi