"The Messenger of Allah said: 'Do not pray for death or wish for it. Whoever insists on praying for it let him say: Allahumma ahini ma kanatil-hayatu khairanli wa tawaffani idha kanatil-wafatu khairanli (O Allah, keep me alive so long as life is good for me, and cause me to die when death is good for me.)"' (Using translation from Nasāʾī 1822)  

قَالَ رَسُولُ اللهِ ﷺ «لَا تَدْعُوا بِالْمَوْتِ وَلَا تَتَمَنُّوهُ فَمَنْ كَانَ دَاعِيًا لَا بُدَّ فَلْيَقُلِ اللهُمَّ أَحْيِنِي مَا كَانَتِ الْحَيَاةُ خَيْرًا لِي وَتَوَفَّنِي إِذَا كَانَتِ الْوَفَاةُ خَيْرًا لِي»  

I came to Khabbab who had been branded with seven brands(1) and he said, "Had Messenger of Allah ﷺ not forbidden us to invoke (Allah) for death, I would have invoked (Allah) for it." (Using translation from Bukhārī 6349)  

أَنَّ رَسُولَ اللهِ ﷺ «نَهَانَا أَنْ نَدْعُوَ بِالْمَوْتِ لَدَعَوْتُ بِهِ»