Prophet (SAW)'s Prayers When tired of life

Due to difficulty death is sought but one should never pray for death instead pray this:

اللَّهُمَّ أَحْيِنِي مَا كَانَتِ الْحَيَاةُ خَيْرٌ لِي وَتَوَفَّنِي إِذَا كَانَتِ الْوَفَاةُ خَيْرَاً لِي

"O Allah keep me alive as long as is good for me and when death is better for me lift me". (Mishkat)