He claims that it is not obligatory to follow the Prophet in everything
Question

What do you think of someone who says that it is not obligatory to follow the Prophet (blessings and peace of Allah be upon him) in everything, because he was human and he may try to work something out, then get it wrong or get it right?
Praise be to Allah.Obeying the Prophet (blessings and peace of Allah be upon him) is obligatory; in fact it is one of the fundamentals of faith, as the Quran indicates. Allah, may He be exalted, says (interpretation of the meaning):
{O you who believe, obey Allah, and obey the Messenger, and those of you who are in authority. If you are in dispute over any matter, refer it to Allah and His Messenger, if you [truly] believe in Allah and the Last Day; that is better and more seemly in the end} [an-Nisa’ 4:59]
{Obey Allah, and obey the Messenger, and be on your guard. But if you turn away, then know that the duty of Our Messenger is only to convey the message in the clearest way} [al-Ma’idah 5:92]
{We did not send any Messenger except to be obeyed by Allah’s leave} [an-Nisa’ 4:64].
Allah, may He be exalted, tells us that no one truly believes until he makes the Prophet (blessings and peace of Allah be upon him) judge concerning what he faces in his life of novel events, and he finds no reservation in his heart towards his ruling, and he accepts it wholeheartedly. Allah, may He be exalted, says:
{But no, by your Lord, they will not [truly] believe until they make you [O Muhammad] judge in all disputes between them, then find in their hearts no reservations about your verdicts, but accept them wholeheartedly} [an-Nisa’ 4:65].
Ibn Kathir (may Allah have mercy on him) said in his Tafsir, 2/349:
Regarding the words {But no, by your Lord, they will not [truly] believe until they make you [O Muhammad] judge in all disputes between them}: here Allah, may He be exalted, swears by His divine essence that no one truly believes until he refers judgement to the Prophet (blessings and peace of Allah be upon him in all his affairs, for whatever he rules is the truth which the believer must accept wholeheartedly, both inwardly and outwardly. Hence Allah says: {then find in their hearts no reservations about your verdicts, but accept them wholeheartedly}. That is, when they refer to you for judgement, then they must obey you inwardly and not feel any reservations about your verdict, and they must submit to it both outwardly and inwardly. So they should submit to it completely, without any reluctance, objection or dispute, as it is narrated in the hadith: “By the One in Whose hand is my soul, no one of you truly believes until his inclinations are in accordance with what I have brought.” (End quote)
In his beneficial and blessed book Riyadh as-Salihin, Imam an-Nawawi (may Allah have mercy on him) included a chapter entitled: the Chapter on the command to adhere to the Sunnah and the etiquette learned therefrom.
In this chapter, he quoted a number of verses from the Quran which are indicative of this important principle of faith, as clear evidence in which there is no confusion or doubt:
Allah, may He be exalted, says:
{Whatever the Messenger gives you [of the gains, or of instructions], accept it, and whatever he forbids to you, refrain from it} [al-Hashr 59:7]
{nor does he speak of his own accord;
It is but divine inspiration} [an-Najm 53:3-4]
{Say: If you love Allah then follow me; Allah will love you and forgive you your sins} [Al `Imran 3:31]
{Verily, in the Messenger of Allah you have a good example for those who look with hope to Allah and the Last Day} [al-Ahzab 33:21]
{But no, by your Lord, they will not [truly] believe until they make you [O Muhammad] judge in all disputes between them, then find in their hearts no reservations about your verdicts, but accept them wholeheartedly} [an-Nisa’ 4:65]]
{If you are in dispute over any matter, refer it to Allah and His Messenger} [an-Nisa’ 4:59].
The scholars said: What is meant is referring to the Quran and Sunnah.
And Allah, may He be exalted, says:
{He who obeys the Messenger has obeyed Allah} [an-Nisa’ 4:80]
{And indeed, [O Muhammad], you guide to a straight path,
The path of Allah} [ash-Shura 42:52-53]
{So let those who go against his command beware lest some calamity strikes them or a painful punishment befalls them} [an-Nur 24:63]
{And remember what is recited in your houses of the verses of Allah and wisdom} [al-Ahzab 33:34]
and there are many similar verses. (End quote).
In the same chapter, he also quoted a number of hadiths from the Prophet (blessings and peace of Allah be upon him) which affirm this principle. These hadiths include the following:
It was narrated from Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “All of my ummah will enter Paradise except those who refuse.” It was said: Who would refuse, O Messenger of Allah? He said: “Whoever obeys me will enter Paradise and whoever disobeys me has refused.” (Narrated by al-Bukhari) It is very strange for someone to claim that following the Prophet (blessings and peace of Allah be upon him) is not obligatory, when Allah, may He be exalted, has connected guidance and success to following and obeying him (blessings and peace of Allah be upon him). Allah, may He be exalted, says:
{So believe in Allah and His Messenger, the unlettered prophet, who believes in Allah and His words, and follow him that you may be guided} [al-A`raf 7:158]
{If you obey him, you will be rightly guided. The duty of the Messenger is only to convey the message in the clearest way} [an-Nur 24:54].
One of the things that the Muslim must believe is that the Sunnah of the Prophet (blessings and peace of Allah be upon him), which is his path – meaning his words and actions regarding religious matters – is infallible.
If the Prophet (blessings and peace of Allah be upon him) made a decision on the basis of his personal opinion, and it turned out to be incorrect, revelation would come down straightaway to correct it and show what Allah wanted and what His ruling was concerning a specific, new development. This is what is proven in the Quran, in passages such as the following:
{It is not befitting for a Prophet to take captives until he has thoroughly suppressed [the enemy] in the land. You desire the fleeting gains of this world, but Allah desires [for you] the hereafter. And Allah is Almighty, Most Wise.
Were it not for a prior decree from Allah, a grievous punishment would have befallen you for what you took [of ransom].
So enjoy what you have gained in war as lawful and good, but fear Allah; verily Allah is Oft-Forgiving, Most Merciful}
[al-Anfal 8:67-69]
{It is not for the Prophet and those who have believed to ask forgiveness for the polytheists, even if they were relatives, after it has become clear to them that they are companions of Hellfire
And the request of forgiveness of Abraham for his father was only because of a promise he had made to him. But when it became apparent to Abraham that his father was an enemy to Allah, he disassociated himself from him. Indeed was Abraham compassionate and patient} [at-Tawbah 9:113-114]
{O Prophet, why do you prohibit [for yourself] that which Allah has made lawful for you, seeking to please your wives? Allah is Oft-Forgiving, Most Merciful.
Allah has already prescribed for you a way of releasing yourselves from your oaths. Allah is your Guardian, and He is All-Knowing, Most Wise} [at-Tahrim 66:1-2].
Conclusion: the one who raised this objection has not understood anything about following the Prophet (blessings and peace of Allah be upon him) and the importance thereof in the religion of Allah, may He be glorified and exalted. He has not understood the evidence that points to that, and when he objected to this fundamental principle, he has not objected with something that will benefit him or that has anything to do with the issue under discussion.
Would that this doubter, if he is confused about something, would refer the matter to people of authority, such as the scholars and jurists, so that they could respond to the doubt that he has in his mind.
May Allah show us the path of guidance and enable us to follow it.
And Allah knows best.