The belief that Allah could’ve taken The Prophet as his son is kufr.
I have a article explaining the meaning of Allah’s sayings found within the Qur’an that he “could have had a son” (Click Here)
It is also kufr to believe The Prophet ﷺ is perfect in every aspect (he is only perfect when it comes to conveying the message and revelation), we know from the Qur’an the prophet made minor sins, and we have an ijmaa on the prophets committing minor sins, but being free from major sins.
Surah Ghafir verse 55: So be patient ˹O Prophet˺, ˹for˺ Allah’s promise is certainly true. Seek forgiveness for your sin (لِذَنۢبِكَ). And glorify the praises of your Lord morning and evening.
Also the reason why Surah Abasa was revealed was because The Prophet ﷺ made a mistake when he ignored the blind man named ʿAbdullah ibn Umm Maktūm, when he came to him seeking guidance, but the Prophet was busy speaking to some of the elite from Quraysh.
Another example is in Surah Tahrim where The Prophet ﷺ forbade honey from himself when it was made halal and Allah ﷻ corrected him and asked him rhetorically in verse 1: O Prophet! Why do you prohibit ˹yourself˺ from what Allah has made lawful to you, seeking to please your wives? And Allah is All-Forgiving, Most Merciful.
Translation: In one of my sermons, a beautiful subtle point was inspired to me (that is, it came to my heart). Remember it well. It is this: all perfections and virtues are perfectly and completely found in the presence of the Messenger, peace and blessings be upon him. The explanation of this is that when someone who possesses power or control does not give a blessing or gift to another, it can only be due to one of four reasons:
The first is that the giver has no ability to give that blessing.
The second is that they do have the ability to give it, but they are miserly or hold back due to some preventer or barrier.
The third is that the one being denied is not deserving or qualified to receive it.
The fourth is that the one being denied is indeed deserving, but there is someone even more beloved to the giver, for whom the blessing is being reserved.
Now in the attribute of Lordship and Godhood, there is a perfection that is beyond the scope of divine power, meaning it belongs to Allah alone and is not within the category of what can be bestowed. All other perfections besides this are within Allah’s power to give.
And Allah, the Most Generous of all generous ones, is more generous than anyone from every angle, and the Messenger of Allah, peace and blessings be upon him, is worthy of every excellence and perfection. Furthermore, there is no one more beloved to Allah than the Messenger, peace and blessings be upon him.
Therefore, it is necessary that under Godhood, all virtues, all degrees of perfection, all blessings, and all forms of goodness that are within divine power must have been granted to the Messenger, peace and blessings be upon him, in the most complete and perfect way. If the attribute of Godhood itself had been something that could be given, it too would have been given to him.
As Allah said in the Quran: “If We had wished to take for Ourselves a son (tafsir shows لَهْوًۭا means son), We would surely have taken it from what is with Us, if We were to do such a thing.” (al-Anbiya: 17)
It is as if this verse is addressing the Christians who claim that Allah has taken a son, and the Jews who said that Uzayr is the son of Allah, and the Arab idolaters who ascribe angels as daughters to Allah. It is saying to them: if we ever intended to take for Ourselves a beloved or a chosen one, we would never choose those you claim. We would only choose the one most beloved to Us, and that is Muhammad, peace and blessings be upon him.
Malfūẓāt A‘lā Ḥaḍrat Pg 226-227
