After the death of Khadijah, Muhammad had about 16 (+/-) wives and slave women, but he got no children from any of them.

Sahih Muslim, Hadith 2771:

Anas reported that a person (a Coptic slave whose name was "Mabur" and he was the cousin of Maria al-Qibtiyya) was charged with fornication with the slave girl of Allah's Messenger (i.e. Maria al-Qibtiyya). Thereupon Allah's Messenger said to 'Ali: Go and strike his neck. 'Ali came to him and he found him in a well making his body cool. 'Ali said to him: Come out, and as he took hold of his hand and brought him out, he found that his sexual organ had been cut. Hadrat 'Ali refrained from striking his neck. He came to Allah's Apostle and said: Allah's Messenger, he has not even the sexual organ with him.

Imam Hakim recorded the following tradition in his book al-Mustadrak (link):

«عن عايشة قالت : اهديت مارية إلى رسول اللّه ومعها ابن عم لها . قالت : فوقع عليها وقعة فاستمرت حاملا . قالت : فعز لها عند ابن عمها . قالت : فقال اهل الافك والزور : «من حاجته إلى الولد ادعى ولد غيره» وكانت امّه قليلة اللبن فابتاعت له ضائنة لبون فكان يغذى بلبنها فحسن عليه لحمه . قالت عايشة : فدخل به علىّ النبى صلى الله عليه وآله وسلم ذات يوم فقال : «كيف ترين»؟ فقلت : من غذى بلحم الضأن يحسن لحمه . قال : «ولا الشبه» قالت : فحملنى ما يحمل النساء من الغيرة أن قلت : ما أرى شبها . قالت : وبلغ رسول اللّه ما يقول الناس فقال لعلى ... ».

Aisha said: " Maria" was presented to the prophet of Islam (as a slave woman) and her cousin (a coptic male slave) was with her. After a while Maria became pregnant. Upon that, the people started slandering that since he [the prophet of Islam] needed child, he related the son of that slave-man to himself. Since Maria, as a mother, didn’t have enough breast milk, they fed him by sheep 's milk that’s why he (the son Ibrahim) was fat. 'Aisha said: Once the prophet brought him to me and asked what I thought about him, I replied, "everyone fed by sheep 's milk will get fat." The holy prophet said doesn’t he look like me? Aisha said, "I jealously said "No"." and then the prophet heard of the untrue accusations of people toward Maria. Upon that the prophet sent Ali to kill her cousin (i.e. the Coptic slave) ...

Hence, when it comes to Muhammad's personal life, then:

  • Muhammad did not give the Coptic slave a chance to have a fair trial in court.
  • He didn’t ask the people (who accused that Coptic slave) to bring the 4 witnesses for fornication. 
  • Furthermore, all the companions who falsely accused the slave and Mariyah of fornication should have received 80 lashes, as per the Islamic punishment of "حد القذف." Their testimonies should have been invalidated in court from that point onward. This aligns with Muhammad's own actions during the incident of Ifk involving 'Aisha, where he lashed all the Sahaba who made false accusations of fornication against her.
  • According to Islamic law, the prescribed punishment for fornication in the case of slaves is 50 lashes. However, Muhammad deviated from Sharia and ordered the direct execution of the slave.

Considering that Muslims claim Muhammad to be the epitome of exemplary behavior, shouldn't the best example adhere to the established rules so that people can follow suit?

This raises the question of why honor killings still occur in Muslim countries. If the leader himself did not adhere to the rules, it is likely that the followers would follow suit.

Some Muslims have tried to justify this by suggesting that Muhammad may have been aware that he lacked a sexual organ. However, even if we assume this to be true, he would have had two options:

  • Firstly, if he had prior knowledge of his condition, he should have taken no action against the Coptic slave, as he would have known the individual was innocent.
  • Secondly, if he still wished to take action despite being aware of the reality, he should have followed the proper legal procedures and initiated a court trial.

In reality, Muhammad was not only accusing the Coptic slave of fornication but indirectly accusing Mariyah as well. Even after Ali informed Muhammad that the Coptic slave was without a sex organ, Muhammad continued to doubt Mariyah's fidelity and questioned the parentage of Ibrahim. Ultimately, Jibrael had to intervene and confirm that Ibrahim was indeed Muhammad's son.

Ibn Kathir recorded the following tradition (link):

عن أنس قال‏:‏ لما ولدت مارية إبراهيم كاد أن يقع في النَّبيّ صلَّى الله عليه وسلَّم منه شيء حتَّى نزل جبريل عليه السلام فقال‏:‏ ‏(‏‏(‏السلام عليك يا أبا إبراهيم‏)‏‏)‏‏.
Anas said, when Ibrahim was born to Maria, then Muhammad became doubtful if Ibrahim was really his son or not. Upon that angel Jibrael came to him and said: Peace be upon you, O the Father of Ibrahim (i.e. confirmed to him that Ibrahim was indeed his son). 

Actually, there exists absolutely no Jibrael, and Muhammad had to use the name of revelation and Jibrael in order to keep the Sahaba quiet. 

Moreover, this tradition is also proof that Muhammad didn't know previously if the Coptic slave had a sexual organ or not, while he kept on doubting Mariyah even after Ali told him that the Coptic slave didn't fornicate with Mariya due to his inability. Therefore, the prime suspect in the eyes of Muhammad was Mariyah.  

These rumours continued till the time of the death of Ibrahim. Thus, on his death, Muhammad was unintentionally claiming that Ibrahim was indeed his son. 

Sahih Muslim:

فلما توفى إبراهيم قال رسول الله صلى الله عليه وسلم ان إبراهيم ابني وانه مات في الثدي وان له لظئرين تكملان رضاعه في الجنة

"...  Ibrahim is (indeed) my son and he dies as a suckling babe. He now has two foster-mothers who would complete his suckling period in Paradise." 

There were doubts surrounding Muhammad's fertility, especially considering that according to Muslim scholars, he married Khadija, who was 40 years old at the time. It is widely accepted that all of Muhammad's children, except Ibrahim, were born from his marriage with Khadija. This raises the question of how he had only one child from numerous young women but had six children with one older woman.

Muslim Excuse: This was the punishment for Insulting Muhammad for "Entering his private chamber"

One Islam apologist wrote (link):

The actual wording of the hadith says أم ولد which means that it refers to Mariyah al-Qibtiyyah, the mother of the Prophet's son Ibrahim. The accused was a person who had accompanied her from Egypt, sometimes claimed to be her cousin. He would visit her too often and people speculated that he was attracted to her and had relations with her. It is inferable that he persisted even though he knew of the rumors about him and had previously been warned about his inappropriate behavior ... Entering in the private chamber of the Prophet's Umm al-Walad and being alone with her repeatedly would be basis enough for a Ta'zir punishment and that much would have been proven through the reports of witnesses who had informed the Prophet in the first place. Insult to the prophet is punishable by death ... The evidence criterion for Insult and Ta'zir is different from that of fornication.

Answer:

If Islam apologists are true that it was the Ta'zir punishment for insulting Muhammad by entering his chamber (and not fornication), why then Ali didn't kill him for this insult in the end? His so-called crime of insulting Muhammad by entering the Chamber of Muhammad despite so-called warnings didn't end with him not having the sexual organ. 

Giving no punishment to that slave person is proof enough that it had nothing to do with the so-called accusation of "insult" by the Islam apologists, but it had to do with the accusation of fornication. 

It is apparent that the notion of a "previous warning" against the slave is simply fabricated by the Islam apologists themselves.

Actually, these Islam apologists don't realize that by claiming that that slave man used to enter in the chamber with Mariyah al-Qubtiyya, they are in fact insulting their Prophet themselves by accusing him of indecent behaviour, where he let that person visit Mariyah and didn't stop him, or to Mariyah to meet each other in his chamber. 

Therefore, if they were really meeting each other in his chamber, then it was the duty of Muhammad and he should have forbidden him from visiting her. And if they claim prophet Muhammad didn't stop them from meeting each other in his chamber while Mariyah was a slave, then how come that became an act of insult to Muhammad in the case of that slave man? After all, then it is Halal in Sharia to meet the slave girls of other men in the chambers and Muhammad didn't stop him to visit Mariyah. 

In conclusion:

Have you heard the story of the lamb and the wolf, where the cunning wolf wanted to eat the lamb by making false accusations against him? The wolf initially blamed the lamb for dirtying his drinking water, even though the water was flowing from the wolf to the lamb. Then the wolf made the next accusation that the lamb had abused him last year, even though the lamb was not yet born. Finally, the wolf came up with the accusation that it was the lamb's father who had abused him last year, using it as an excuse to eat the lamb.

These Islamic apologists are similar to that cunning wolf, making false accusations repeatedly against the innocent in order to further their own sinister agenda.