Ṣaḥīḥ reporting in supplication and praising Allah the almighty

«اللَّهُمَّ رَبَّنَا آتِنَا فِي الدُّنْيَا حَسَنَةً، وَفِي الآخِرَةِ حَسَنَةً، وَقِنَا عَذَابَ النَّارِ»
{وهو أكثر دعاء النبي صلى الله عليه وسلم}

allahumma rabbana atina fi d-dunya hasanah, wa fi l-akhirati hasanah, wa qina ʾadhaba n-nar

"O Allah! Give to us in the world that which is good and in the Hereafter that which is good, and save us from the torment of the Fire."

It is the most repeated supplication of the Prophet PBUH.