It's reasonable to analyze the arguments that would insist Maria was a concubine and see if it can deconstruct. First, Maria is not mentioned by name in the Quran. In contrast, the narratives in Islamic history indicated that Prophet Muhammad (PBUH) can be presumed to marry Maria. She is one of the examples to prove that, when a woman is kept as a slave girl and she gives birth to a child for her master, then she automatically becomes freed, after the death of her master. Maria was a prime example because after Prophet Muhammad (PBUH) died, she was declared to be free.
Sometimes, people need to be careful with narratives in Islamic history.
Scholars like John Burton is a prime example. Sometimes, Muslim scholars in the early period, wanted precedents to prove a certain law that they were arriving. Sometimes, the law may have been arrived at as a reasonable principle, but they want some grounding in a precedent. They would find in the life example of Prophet Muhammad (PBUH) if it's not to be found there, sometimes it was manufactured, not by deliberate cheating. People did that too. However, careful scholars did not do that.
However, the careful scholars could have let something slip by, meaning somebody else might have invented something. Therefore, it takes on the appearance of a genuine report that Prophet Muhammad (PBUH) stated.
The careful scholar analyzed and is convinced that's a genuine report. They incorporate that all into the whole system of thought. It could have happened in the case of Maria. Specifically, people need to think about the slave girl who gave birth to a child for her master. Indeed, she did a good thing for the Muslim society. How can we continue to treat her as a slave, even after the death of her master? She shouldn't have bred special status, even within the lifetime of her master. She will be treated with some honor and recognition because she has done well for her master in bringing a child into the world. Maybe within the lifetime of her master, she was already treated as a wife in the general description of a concubinage.
There were all these possibilities, levels, and gradations of how close a woman might be as a concubine to the wife status. Truly, Maria achieved that wife status. Maria could have been more widely recognized as being a free person after the death of Prophet Muhammad (PBUH). Muslim scholars need a precedent, she became freed by virtue that she gave birth to Prophet Muhammad’s (PBUH) son. This becomes a precedent for other such cases too. Within that thought system, things might have become circular, she becomes the proof of that principle, but the principle may have generated the proof.
Therefore, people should not insist on that thought because one doesn’t know. For the modern Muslim, who is having great difficulty in thinking that a man is allowed to sleep with his concubine, just because he owns her as a slave girl, this is hard for Muslims to accept nowadays. If a Muslim is a burden with this as a real problem, here is one way of thinking about this, so that one is not overburdened with this because one knows that the argument can go both ways. It can be argued this way, it can be counterargued this way, and even the counterargument can be deconstructed.
Does that mean Maria could have been manufactured?
This can be taken as a two-stage approach. In one stage, the assumption is that she existed as Islamic tradition says, and she was brought to live with the Prophet Muhammad (PBUH) as the Islamic tradition says and was she married to him or not. However, a deeper level of analysis is possible too.
Some Academic scholars have looked at whether Prophet Muhammad (PBUH) existed. There was a European man, named Sven Kalisch, who was mentioned to Dr. Shabir Ally in a debate with a Christian person. He said, “Prophet Muhammad (PBUH) did not exist.” Yet, he was not taken as an authority on this question. As a result, it did not lead anywhere. The idea was that Prophet Muhammad (PBUH) did not exist based on some very shoddy sort of scholarship. Nowadays, academic scholars do say that Prophet Muhammad (PBUH) existed. Despite if they're not agreeing with all the Islamic traditions about him.
There is another person, named Robert Spencer, who wrote a book called, Did Muhammad exist? He suggested that Prophet Muhammad (PBUH) did not exist. To sum, Muslims know that Prophet Muhammad (PBUH) existed because he left so many traces. He left children, grandchildren, and great-grandchildren etc.
Meanwhile, the Islamic records were being put together, it's quite clear. Prophet Muhammad (PBUH) existed in history. Likewise, Maria who died five years after Prophet Muhammad (PBUH). That's long before the Islamic traditions were put into writing. During the Islamic traditions are put into writing, she is a vague memory. How does one know that she existed? Perhaps she's not a vague memory, maybe she is a manufactured memory. What material traces did she leave behind? She had a son, but the son died, in its infancy, even before she died. If the son was set to be 18 months old. When he passed away, this would have been a beloved child in the community. Prophet Muhammad (PBUH) did not have a son at that time. Previously, he had sons through Khadijah, his first wife, but those sons died in infancy. Did they exist? Allegedly, this son has been born within the last few years of Prophet Muhammad's (PBUH) life when he was in his fifties.
The community was very strong as well. The community would have been so excited about the child. For instance, people may report their experiences by holding and playing with the child. However, there is very little information about the baby, Ibrahim.
Did he exist or is this something that the Muslims are imagining? There is more detail on how people imagine things based on what is mentioned in the Quran. According to the Quran in Surah 33, it states, “Muhammad is not the father of any one of you men; He is God’s messenger and the seal of the prophets.” Quran [33:40].
People may think that he was the father of a child who died in infancy. To sum, is not that Maria is an invention, or that her son Ibrahim was an invention. However, if a Muslim is overburdened with the thought that Prophet Muhammad (PBUH) had a concubine, then one can counter with what was mentioned earlier. On the other hand, if a person believes that Muhammad (PBUH) had a concubine, then one can question that individual’s statement. For instance, one can ask, “How do you know that it’s really a fact that she and her son existed?” “How was she kept as Prophet Muhammad (PBUH) as a concubine but not as a married wife?”