Imam Ibn Al-Qayyim, may Allah have mercy upon him, said:

The Ummah of Muhammad, peace and blessings of Allah be upon him, does not require anyone after him; their sole necessity is for someone to convey his teachings. The message of Muhammad is all-encompassing, universal, and (perfectly) preserved. This universality, comprehensiveness, and preservation are not confined to any (specific time, place, or circumstance); instead, they extend to all those to whom Muhammad was sent, as well as addressing all the fundamental and subsidiary matters of the religion.

Muhammad’s message is sufficient, all-encompassing, and universal—there is no requirement for anything beyond it. It has addressed every aspect of truth necessary for his Ummah in their knowledge and actions. Allah’s Messenger, peace and blessings of Allah be upon him, did not depart from this world without imparting to his Ummah all that they needed to know. He taught them the etiquettes of using the toilet, sexual relations, the etiquettes of sleep and waking, eating, drinking, and traveling. He acquainted them with the etiquettes of speech and silence; the etiquettes of keeping company with the people and seclusion. He acquainted them with matters regarding illness, good health, poverty and wealth, and all matters regarding life and death.

He described Allah’s throne, the angels, the jinn, the fire of hell, and the Day of Judgment in a way that made them feel as though they were witnessing these realities with the naked eye. He conveyed knowledge about their Lord, His Perfect Names and Attributes, emphasising that Allah is the only One who deserves their worship. He acquainted them with the ancient Prophets and their respective nations- the events that transpired between them as if one were witnessing those moments firsthand. He informed them of all the avenues leading to righteousness and the various paths of wrongdoing, both broadly and specifically, in a manner that no other prophet had conveyed to his people. He acquiainted them with death and will take place in the grave, whether they be of joy or torment. Additionally, he presented the evidences and proofs of Tawhid (pure Islamic Monotheism). He acquainted them with Prophethood and the matters concerning the Afterlife, while also countering all factions of disbelief and misguidance. He acquainted them with war strategies- how to confront the enemy, the way to achieve victory and conquests. If they were aware of and comprehended these matters appropriately, they would not be defeated by their adversary.

He acquainted them with the schemes of Iblees, the methods by which he seeks to influence them, and the strategies to counteract those schemes and plans. He acquainted them with the soul- its characteristics and faults- in such a manner that they are not in need of anyone else to tell them about it.

He instructed them on how to navigate their everyday existence, and had they recognized and implemented his teachings, their worldly matters would have been securely established. He provided them with all the means necessary for success in both this life and the hereafter, rendering them independent of any other guidance. Therefore, it is unfounded to assert that the path of Muhammad requires any external support. Such claims stem from a limited and insufficient understanding on the part of the individual. Allah said:

أَوَلَمْ يَكْفِهِمْ أَنَّا أَنزَلْنَا عَلَيْكَ الْكِتَابَ يُتْلَىٰ عَلَيْهِمْ ۚ إِنَّ فِي ذَٰلِكَ لَرَحْمَةً وَذِكْرَىٰ لِقَوْمٍ يُؤْمِنُونَ

Is it not sufficient for them that We have sent down to you the Book (the Qur’an) which is recited to them? Verily, herein is mercy and a reminder (or an admonition) for a people who believe. [29:51]

Allah [The Most High] said:
وَنَزَّلْنَا عَلَيْكَ الْكِتَابَ تِبْيَانًا لِّكُلِّ شَيْءٍ وَهُدًى وَرَحْمَةً وَبُشْرَىٰ لِلْمُسْلِمِينَ

And We have sent down to you the Book (the Qur’an) as an exposition of everything, a guidance, a mercy, and glad tidings for those who have submitted themselves (to Allah as Muslims)]. [16:89]

Allah [The Most High] said:
يَا أَيُّهَا النَّاسُ قَدْ جَاءَتْكُم مَّوْعِظَةٌ مِّن رَّبِّكُمْ وَشِفَاءٌ لِّمَا فِي الصُّدُورِ وَهُدًى وَرَحْمَةٌ لِّلْمُؤْمِنِينَ

O mankind! There has come to you a good advice from your Lord [i.e. the Qur’an, ordering all that is good and forbidding all that is evil], and a healing for that [disease of ignorance, doubt, hypocrisy and differences, etc.] in your breasts, – a guidance and a mercy [explaining lawful and unlawful things, etc.] for the believers. [10:57]

An Excerpt from “i’lam al-muwaqqi’in 4/375-377