Anyone who offends the Prophet must be killed

From Islam Q&A:

...A blind man had a female slave who had borne him a child (umm walad) who reviled the Prophet (peace and blessings of Allaah be upon him) and disparaged him, and he told her not to do that but she did not stop, and he rebuked her but she paid no heed.

One night she started to disparage and revile the Prophet (peace and blessings of Allaah be upon him), so he took a dagger and put it in her stomach and pressed on it and killed her. There fell between her legs a child who was smeared with the blood that was there.

The next morning mention of that was made to the Prophet (peace and blessings of Allaah be upon him) and he assembled the people and said: “I adjure by Allaah the man who did this to stand up.”

The blind man stood up and came through the people, trembling, and he came and sat before the Prophet (peace and blessings of Allaah be upon him). He said: O Messenger of Allaah, I am the one who did it. She used to revile you and disparage you, and I told her not to do it but she did not stop, and I rebuked her but she paid no heed. I have two sons from her who are like two pearls, and she was good to me. Last night she started to revile you and disparage you, and I took a dagger and placed it on her stomach and I pressed on it until I killed her.

The Prophet (peace and blessings of Allaah be upon him) said: “Bear witness that no retaliation is due for her blood.”

Narrated by Abu Dawood (4361) and others. In the answer to question no. 103739 we have explained that the basis of this story is saheeh and that it has been narrated in several versions which, when taken together, indicate that the incident did indeed take place, despite the variations in some reports.

This woman was not killed because she was a dhimmi, rather it was because she reviled the Messenger of Allaah (peace and blessings of Allaah be upon him), so she deserved to be executed for that reason, and if she was a Muslim, she became a kaafir by this action, and deserved to be executed for that reason too. [...]