The Glorious Qur’an is the very Word of Allah revealed to His Messenger, Muhammad (peace and blessings be upon him). The authenticity and divinity of the Qur’an are unquestioned, and there is no difference among Muslims on this fact. The Holy Qur’an has reached us through the process of tawatur (historical continuity and perpetuation achieved through transfer from generation to generation). When we say that the Qur’an has reached us through tawatur, we imply that so many people in every generation conveyed it to the next and so on that there can be no doubt about its authenticity.
The prominent Muslim scholar, Dr. Muhammad Abu Laylah, professor of the Islamic Studies & Comparative Religions at Al-Azhar University states:
“First, we draw your attention to some facts that can help you greatly understand and form the answer yourself:
1. These verses are no different in nature from the rest of the verses of this surah, either in style or in rhetoric, or in impetus and other thematic features or characteristics. They are all stamped by the Qur’an and they all are Allah’s words.
2.It is Allah, not Muhammad, Who says to people that they should keep their manners in approaching the Prophet (peace and blessings be upon him) or visiting him. In other words, Allah relieves Muhammad (peace and blessings be upon him) from telling people because they may misunderstand him or find way to twist his words.
3.Every word of the Qur’an is of universal nature though it may look local or limited to a certain time and space or to a certain group of people. The universal quality of these verses is to show people to be polite and to be well-mannered in dealing with their Prophet (peace and blessings be upon him) or his successors or his scholars who stand for his religion later on.
4.Concerning your doubt about the clause of the verse concerning the wives of Prophet (peace and blessings be upon him) not to be married after him, this command was strictly limited to the Prophet (peace and blessings be upon him). Though this ruling may look to be local, it is universal if put in the whole context. Moreover, there are some other verses in which Allah, for example, put blame on the Prophet (peace and blessings be upon him) or drew his attention to something other than what he was thinking of. This does not mean that he was reproaching or blaming himself or objecting to himself. At the time these verses were revealed, Muhammad (peace and blessings be upon him) had the power to say this in his own words. He had full authority over Muslims. Muhammad was the most truthful person who ever lived on this planet. He was in no need to support himself by lies or fabrications. Muhammad, by the power of truth, built a great Ummah, spread his religion in a very short time and by peaceful means to all of Arabia, and in the twenty-five years after his death Islam spread in Asia and Africa. Now, Islam is the fastest growing religion in the world. This is due to Muhammad’s truthfulness and sincerity and love of humanity.