In The Name of Allah, The Most Merciful The Bestower of Mercy.

He replied: It is not permissible to utter speech (unrestrictedly) concerning prolongation of one’s stay in this life because a prolongation of one’s life can either be upon good or evil. Indeed, the most evil of people are those whose lives are prolonged while their actions are evil.  Therefore, with regards to this matter, if one were to say: “May Allah prolong your stay (in this life) upon obedience to Him”’, there is no harm in this speech. [Source: Al-Manahi Al-Lafdhiyyah page: 25]

Supplication:

We ask Allah:

اللَّهُمَّ بِعِلْمِكَ الْغَيْبَ وَقُدْرَتِكَ عَلَى الْخَلْقِ أَحْيِنِي مَا عَلِمْتَ الْحَيَاةَ خَيْراً لِي وَتَوَفَّنِي إِذَا عَلِمْتَ الْوَفَاةَ خَيْراً لِي، اللَّهُمَّ إِنِّي أَسْأَلُكَ خَشْيَتَكَ فِي الْغَيْبِ وَالشَّهَادَةِ، وَأَسْأَلُكَ كَلِمَةَ الْحَقِّ فِي الرِّضَا وَالْغَضَبِ، وَأَسْأَلُكَ الْقَصْدَ فِي الْغِنَى وَالْفَقْرِ، وَأَسْأَلُكَ نَعِيماً لَا يَنْفَذُ، وَأَسْأَلُكَ قُرَّةَ عَيْنٍ لَا تَنْقَطِعُ، وَأَسْأَلُكَ الرِّضِا بَعْدَ الْقَضَاءِ، وَأَسْأَلُكَ بَرْدَ الْعَيْشِ بَعْدَ الْمَوْتِ، وَأَسْأَلُكَ لَذَّةَ النَّظَرِ إِلَى وَجْهِكَ وَالشَّوْقَ إِلَى لِقَائِكَ فِي غَيْرِ ضَرَّاءَ مُضِرَّةٍ وَلَا فِتْنَةٍ مُضِلَّةٍ، اللَّهُمَّ زَيِّنَّا بِزِينَةِ الْإِيمَانِ
وَاجْعَلْنَا هُدَاةً مُهْتَدِينَ

O Allah! By Your Knowledge of the unseen and by Your Power over creation, let me live if life is good for me, and let me die if death is good for me; O Allah! I ask You to grant me (the blessing of having) fear of You in private and public, and I ask You (to make me utter) a statement of truth in times of contentment and anger, and I ask You for moderation when in a state of wealth and poverty, and I ask you for blessings that never ceases, and I ask You for the coolness of my eye that never ends, and I ask You (to make me pleased) after (Your) decree; and I ask You for a life of (ease, comfort, tranquillity, etc) after death; I ask You for the delight of looking at Your Face (i.e. in the Hereafter) and yearning to meet You without any harm and misleading trials (coming upon me). O Allah! Adorn us with the adornment of Iman, and make us (from those who are) guided and guiding (others). [As-Saheehah Number 1301]