O Allah, keep me alive as long as life is good for me, and cause me to die when — Daily Supplications
اللَّهُمَّ أَحْيِنِي مَا كَانَتِ الْحَيَاةُ خَيْرًا لِي وَتَوَفَّنِي إِذَا كَانَتِ الْوَفَاةُ خَيْرًا لِي
Transliteration: Allaahumma ahyinee maa kaanatil-hayaatu khayran lee wa tawaffanee idhaa kaanatil-wafaatu khayran lee
Translation: O Allah, keep me alive as long as life is good for me, and cause me to die when death is better for me.
Reference: Bukhari 7:158, Muslim 4:2083