Are children born to non-Muslim parents who have not entered into a legitimate marriage contract according to Islamic Sharia considered illegitimate?

First: Islam upholds the validity of the marriages of disbelievers that are considered sound according to their own laws. The rulings of a valid Islamic marriage, such as the establishment of lineage and inheritance, apply to them. Indeed, the Prophet, peace and blessings be upon him, upheld the marriages of those who embraced Islam.

Second: If a marriage is valid according to Islamic law, then it is considered valid. If it is invalid, it can be upheld under two conditions: that the disbelievers believe in its validity according to their own laws, and that they do not refer their dispute to us. Otherwise, they must be separated.

Third: Children born from the marriages of disbelievers that they consider valid are attributed to their fathers. However, if the union was merely a relationship without marriage, then they are children of fornication. Nevertheless, if the fornicator acknowledges them as his own, they are his children, and their maintenance is obligatory upon him.