Did Muhammad (peace be upon him) claim that no prophets would come after him?
Is it in the Koran? If so, does that mean no one who comes after him will have the gift of prophecy?
Yes. It is in the Quran. And also, just have a thorough study on all of those who claimed to be prophets after him and you will find that they were just absurd!
And as of prophesy, in Shia Islam we believe that God has chosen twelve imams as successors of Muhammad.
And Yes. An Imam can be higher than a prophet.
However. We believe that Muhammad was the best of all God's creations.
Here is the related Quranic verse:
"Muhammad is not the father of [any] one of your men, but [he is] the Messenger of Allah and last of the prophets. And ever is Allah, of all things, Knowing." Quran 33:40.
Also, Why is it not okay to criticize the prophet? Surely he made mistakes... can't a person, even a Muslim, be critical and say marriage of a middle-aged man to a prepubescent girl is low and should be outlawed?
Even if a person accepts him as a prophet, can't they also say he made serious mistakes?
The story of the prophet marriage of Aysha when Aysha was a child is a made up story.
Aysha was a divorcee when the prophet married her.
I talked about this before.
However let me say this..
Whoever will read the Quran and the biography of prophet Muhammad will realize that he was not a man who is after earthly pleasures and young women..
His first wife was 15 years older than him..
She was a great woman who supported Islam with here great wealth..
As of Aysha, she was the daughter of Abu Bakr,
According to Shia Islam,
Abubakr is "Apostle Paul" of Islam! However keep in mind that we believe that Apostle Paul was devil man who corrupted Christianity..
With respect to our Sunni brothers, let me say that we believe that Abu Bakr has claimed to be a Muslim because he knew that Islam will succeed..
He was able in coordination with another man and their two daughter (Aysha is one of them) to kill the prophet!
The Quran itself condemned both of these two ladies...
Aysha made up many Sunni Hadiths ..
The Sunni tried to portray a picture of Aysha as the prophet beloved wife who was very close to him...
However, even a famous Sunni scholar who is called Ibn Saad, mentioned in his ancient book, which was a kind of history book, that Aysha was married to another man before she got divorce and married the prophet.
Also, Aysha joined the prophet in his first Battle Badr, and nobody who is younger than 15 was allowed to join..
All in all, prophets don't make mistakes, otherwise, they are not prophets!