It wasnarrated that Abu Hurairah said:
"The Messenger of Allah (ﷺ)saidto a man: 'What do you say during your Salat?' He said: 'TheTashah-hud, then I ask Allah for Paradise, and I seek refuge with Himfrom Hell, but I do not understand what you and Mu'adh murmur(duringSalat). He said: 'Our murmuring revolves around the samethings.'" (RU)
English reference (RU): Vol. 1, Book 5, Hadith 910 (RU)
Arabic reference (RU): Book 5, Hadith 963 (RU)