Abu Malik Ashaja'i reported on the authority of his father that whenever a person embraced Islam, Allah's Messenger (ﷺ) instructed him to recilte:" O Allah, grant me pardon, have mercy upon me, direct me to the path of righteousness and provide me sustenance."
حَدَّثَنَا أَبُو كَامِلٍ الْجَحْدَرِيُّ، حَدَّثَنَا عَبْدُ الْوَاحِدِ، - يَعْنِي ابْنَ زِيَادٍ - حَدَّثَنَا أَبُو مَالِكٍ الأَشْجَعِيُّ عَنْ أَبِيهِ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُعَلِّمُ مَنْ أَسْلَمَ يَقُولُ " اللَّهُمَّ اغْفِرْ لِي وَارْحَمْنِي وَاهْدِنِي وَارْزُقْنِي " .
Muslim
The Book Pertaining to the Remembrance of Allah, Supplication, Repentance and Seeking Forgiveness • Hadith 44