If a person's last words are la ilaha illallah (there is no god but Allah), Islamic tradition states that they are guaranteed Jannah (Paradise).
Significance of La Ilaha Illallah
La ilaha illallah is the core declaration of faith (Shahada) in Islam. It signifies the absolute oneness and uniqueness of Allah and the rejection of all other deities or forms of worship. Saying it sincerely at the time of death reflects a lifetime of faith and devotion, or sincere repentance.
Guarantee of Jannah
According to Islamic teachings, uttering la ilaha illallah as one's last words is a sign of a good ending. This is based on various hadith (sayings and actions of the Prophet Muhammad, peace be upon him). The belief is that Allah, in His mercy, will grant Paradise to the person who dies affirming this fundamental belief.
Conditions
It's important to note that the utterance should be made with understanding and sincerity, not simply as a meaningless repetition. It reflects the individual's belief in the oneness of Allah throughout their life, and their commitment to Islam.
Summary
In essence, if someone dies saying la ilaha illallah with sincerity, it is considered a very positive sign, and in Islamic belief, guarantees them entrance into Jannah (Paradise).