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

Allaah [The Exalted] said:

وَمَن يَرغَبُ عَن مِلَّةِ إِبراهيمَ إِلّا مَن سَفِهَ نَفسَهُ ۚ وَلَقَدِ اصطَفَيناهُ فِي الدُّنيا ۖ وَإِنَّهُ فِي الآخِرَةِ لَمِنَ الصّالِحينَ
إِذ قالَ لَهُ رَبُّهُ أَسلِم ۖ قالَ أَسلَمتُ لِرَبِّ العالَمينَ
وَوَصّىٰ بِها إِبراهيمُ بَنيهِ وَيَعقوبُ يا بَنِيَّ إِنَّ اللَّهَ اصطَفىٰ لَكُمُ الدّينَ فَلا تَموتُنَّ إِلّا وَأَنتُم مُسلِمونَ
أَم كُنتُم شُهَداءَ إِذ حَضَرَ يَعقوبَ المَوتُ إِذ قالَ لِبَنيهِ ما تَعبُدونَ مِن بَعدي قالوا نَعبُدُ إِلٰهَكَ وَإِلٰهَ آبائِكَ إِبراهيمَ وَإِسماعيلَ وَإِسحاقَ إِلٰهًا واحِدًا وَنَحنُ لَهُ مُسلِمونَ
تِلكَ أُمَّةٌ قَد خَلَت ۖ لَها ما كَسَبَت وَلَكُم ما كَسَبتُم ۖ وَلا تُسأَلونَ عَمّا كانوا يَعمَلونَ

And who turns away from the religion of Ibrahim (Abraham) (i.e. Islamic Monotheism) except him who befools himself? Truly, We chose him in this world and verily, in the Hereafter he will be among the righteous. When his Lord said to him, “Submit (i.e. be a Muslim)!” He said, “I have submitted myself (as a Muslim) to the Lord of the ‘Alamin (mankind, jinns and all that exists).” And this (submission to Allah, Islam) was enjoined by Ibrahim (Abraham) upon his sons and by Ya’qub (Jacob), (saying), “O my sons! Allah has chosen for you the (true) religion, then die not except in the Faith of Islam (as Muslims – Islamic Monotheism).” Or were you witnesses when death approached Ya’qub (Jacob)? When he said unto his sons, “What will you worship after me?” They said, “We shall worship your Ilah (God – Allah), the Ilah (God) of your fathers, Ibrahim (Abraham), Isma’il (Ishmael), Ishaque (Isaac), One Ilah (God), and to Him we submit (in Islam).” That was a nation who has passed away. They shall receive the reward of what they earned and you of what you earn. And you will not be asked of what they used to do. [Al-Baqarah. Aayaat 130-134]

Regarding Allaah’s statement:

أَم كُنتُم شُهَداءَ إِذ حَضَرَ يَعقوبَ المَوتُ إِذ قالَ لِبَنيهِ ما تَعبُدونَ مِن بَعدي قالوا نَعبُدُ إِلٰهَكَ وَإِلٰهَ آبائِكَ إِبراهيمَ وَإِسماعيلَ وَإِسحاقَ إِلٰهًا واحِدًا وَنَحنُ لَهُ مُسلِمونَ

Or were you witnesses when death approached Ya’qub (Jacob)? When he said to his sons, “What will you worship after me?” They said, “We shall worship your Ilah (God – Allah), the Ilah (God) of your fathers, Ibrahim (Abraham), Isma’il (Ishmael), Ishaque (Isaac), One Ilah (God), and to Him we submit (in Islam).” [Al-Baqarah 133]

Imaam As-Sadi [may Allaah have mercy upon him] said: When it is the case that the Jews claimed to be following the religion o f Ibraheem and after him Yaqoob [peace be upon them], Allaah [The Exalted] rejected their claim, saying, [أَم كُنتُم شُهَداءَ – Or were you witnesses]- Meaning, (where you) present; [إِذ حَضَرَ يَعقوبَ المَوتُ – when death approached Ya’qub (Jacob)?]- Meaning, in the beginning of the affair and what led to it, when he said to his sons in order to test them and so as to receive the joy – when he is still alive – that they would fulfil that which he commanded them, saying [ما تَعبُدونَ مِن بَعدي – What will you worship after me?] So they replied, [نَعبُدُ إِلٰهَكَ وَإِلٰهَ آبائِكَ إِبراهيمَ وَإِسماعيلَ وَإِسحاقَ إِلٰهًا واحِدًا – We shall worship your Ilah (God – Allah), the Ilah (God) of your fathers, Ibrahim (Abraham), Isma’il (Ishmael), Ishaque (Isaac), One Ilah (God)]- Meaning, neither will we ascribe anything as partners to Him (Allaah) in worship nor declare anyone as His co-equal. [ وَنَحنُ لَهُ مُسلِمونَ – and to Him we submit (in Islam) (see footnote a)], so they combined pure monotheism and deeds (in this response of theirs). (1)

Tawheed at The Time of Departure From This World

Imaam Ibnul Qayyim [may Allaah have mercy upon him] said:
The Shahaadah [i.e. None has the right to be worshipped except Allaah] at the time of death wipes away one’s evil deeds. This is because the one who utters it at the time of departure from this world does so with certainty and knowledge of its true meaning. All his desires [i.e. desire for the worldly life] come to an end and his rebellious soul [becomes] mild and submissive after being in (a state of) refusal and disobedience- a (state of) approval after turning away and a state of humility after being held in high esteem. The [heart’s and the soul’s] eagerness for the worldly life and its merits departs and distances [from everything] whilst in the presence of its Lord, Originator and true Protector; humble in the presence of its Lord, hopeful of pardon, forgiveness and mercy.

Belief in the Oneness of Allaah-[i.e. the belief in the Oneness of Allaah’s Lordship (that Allaah alone is the creator, provider and the one in control of all the affairs of the universe); and that Allaah alone has perfect Names and Attributes and that none is similar to Allaah; and that Allaah alone has the right to be worshipped]-frees and distances the soul from that which leads to Shirk [polytheism] and manifests the reality of its falsity. Therefore, those wishes which the soul busied itself with [in the worldly life] ceases [at the time of departure from this world] and all its concern is [directed towards] the One it is certain to meet [i.e. Allaah].

The person [who is blessed with the ability to utter this testimony of faith] focuses his attention completely on Allaah- turns to Allaah with his soul and desire and submits to Allaah alone, inwardly and outwardly. The person’s hidden affair [i.e. the heart and soul] and outward affair [i.e. what he proclaims] testify to the same thing, so he sincerely says: “None has the right to be worshipped except Allaah.” His heart is freed from attachment to other than Allaah -all the worldly [desires] leaves the heart because he is about to stand in Allaah’s presence. The intensity of his desire [for the worldly life] is extinguished and the heart is filled with the [desire for] the afterlife, and thus it becomes the attention of his eyes and the worldly life is forgotten. [When] this sincere testimony is his last deed, it purifies him from sins and thus Allaah enters [him into a noble position]. That is because he meets Allaah with a truthful and pure testimony, whose outward manifestation is in agreement with [what is hidden in the heart and soul]. If a person made this testimony (with this type of conviction) during the time of well-being [i.e. whilst residing in the worldly life], he would not have placed great importance on worldly desires, rather he would have attached himself to Allaah alone; but [the fact of the matter is that] he made this testimony [in the worldly life] with a heart filled with desires, love of life and its means of subsistence. (2)

We ask Allaah:

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; Aand I ask You for a life of (ease, comfort, tranquility 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 Eemaan, and make us (from those who are) guided and guiding (others). [Sunan An-Nasaa’ee’ Number 1305 & declared Saheeh by Imaam Albaani (rahimahullaah) in As-Saheehah Number 1301]

اللَّهُمَّ أَصْلِحْ لِي دِينِي الَّذِي هُوَ عِصْمَةُ أَمْرِي
وَأَصْلِحْ لِي دُنْيَايَ الَّتِي فِيهَا مَعَاشِي
وَأَصْلِحْ لِي آخِرَتِي الَّتِي فِيهَا مَعَادِي
وَاجْعَلِ الْحَيَاةَ زِيَادَةً لِي فِي كُلِّ خَيْرٍ
وَاجْعَلِ الْمَوْتَ رَاحَةً لِي مِنْ كُلِّ شَرٍّ

O Allah! Rectify my religion for me, which is the safeguard of my affairs; rectify my worldly [affairs], wherein is my livelihood; and rectify my Afterlife to which is my return; and make life for me [as a means of] increase in every good and make death for me as a rest from every evil. [Saheeh Muslim Number: 2720]

Footnote a: https://salaficentre.com/2020/10/18/one-must-call-himself-a-muslim-if-he-truly-follows-the-path-of-the-prophets-and-messengers/

[Ref 1: An Excerpt from Tafseer As-Sadi. slightly paraphrased]
[Ref 2: An Excerpt from ‘Al-Fawaa-id. Page: 91-92. slightly paraphrased]