Whenever anyone accepted Islam, the Prophet (ﷺ) used to teach him how to
pray then he would instruct him to invoke Allah with the following words:
Allāhummaghfir lī, warḥamnī, waḥdinī, wa `āfinī warzuqnī.
Whenever anyone accepted Islam, the Prophet (ﷺ) used to teach him how to pray then he would instruct him to invoke Allah with the following words:
O Allah forgive me, and have mercy on me and guide me and give me good health and provide for me.
Reference:
Muslim 4/2073, and in one of Muslim's reports there is the addition: 'For
these words combine [the goodness of] this world and the next.'