What is the supplication to be recited upon reaching forty years of age?

The noble verses (Al-Ahqaf: 15-16) serve as guidance for anyone who reaches forty years of age to renew their repentance and turning to God, and to increase the supplication mentioned therein. There is nothing in this that implies the obligation of this remembrance, and there is no obligatory supplication except the supplication for guidance in Al-Fatihah.