Hazrat Anas, may Allah be pleased with him, narrated that the most frequent invocation of the Holy Prophet, peace and blessings of Allah be on him, was:
اَللّٰھُمَّ رَبَّنَا آتِنَا فِی الدُّنْيَا حَسَنَةً وَفِی الْآخِرَةِ حَسَنَةً وَقِنَا عَذَابَ النَّارِ
[O Allah, our Lord, grant us the best of this world as well as the best of the life Hereafter and shield us from the torment of the Fire.]
(Sahih al-Bukhari, Kitab al-Da‘wat)