Q 3: I heard a preacher saying that the scholars are of the view that any who wants a good end to his life should frequently supplicate Allah (Exalted be He) saying, "O Ever-Living, O Sustainer, by your mercy I seek help", and persists on reciting Ayat-ul-Kursy (The Qur’anic Verse of Allah's Chair), and the concluding verses of Surah Al-Baqarah. In addition to reciting:
Say (O Muhammad صلى الله عليه وسلم): "O Allâh! Possessor of the kingdom, You give the kingdom to whom You will, and You take the kingdom from whom You will, and You endue with honour whom You will, and You humiliate whom You will. In Your Hand is the good. Verily, You are Able to do all things.
You make the night to enter into the day, and You make the day to enter into the night (i.e. increase and decrease in the hours of the night and the day during winter and summer), You bring the living out of the dead, and You bring the dead out of the living. And You give wealth and sustenance to whom You will, without limit (measure or account).
Allâh bears witness that Lâ ilâha illa Huwa (none has the right to be worshipped but He), and the angels, and those having knowledge (also give this witness); (He always) maintains His creation in Justice. Lâ ilâha illa Huwa (none has the right to be worshipped but He), the All-Mighty, the All-Wise.
After every obligatory Salah (prayer). What is the ruling on the one who recites these verses after the five obligatory daily Salahs in addition to the authentically reported Adhkar (invocations)?
(Part No. 24; Page No. 199)
the permissible Dhikr that can be said after obligatory Salah following the ordinary Dhikr includes reciting Ayat-ul-Kursy, Surah Al-Ikhlas, and Al-Mu`awwidhatayn (Surahs Al-Falaq, and Al-Nas). The last three Surahs should be repeated three times after Fajr (Dawn) Prayer, and Maghrib (Sunset) Prayer. One of the reasons for having a good end to one's life is the inward and outward Istiqamah (integrity) in obeying Allah (Exalted be He). However, we do not have any authentic proof from the Qur'an or the Sunnah of what has been mentioned in your question.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.