All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
A serious threat is confirmed in the authentic Sunnah for whoever enslaves a free person, and the scholars considered this as a grave major sin. Indeed. enslaving free people is one of the greatest forms of injustice and this is worse than stealing money and the like. Therefore, if a person knows that there is such an injustice on a particular person, whether he is a Muslim or a non-Muslim, he should endeavor as much as he can to repel this injustice as this is an act of forbidding evil. Besides, whoever spends some of his money, in order to free someone who was unjustly enslaved, then he is doing good, without doubt, and thus he is doing a great act of getting closer to Allaah for which he is expected to be rewarded in the Hereafter.
As regards whether or not this act is sufficient for expiating for an oath and other matters for which it is legislated to expiate by freeing a slave, then the answer is no, because this person whom you want to help is not a real slave in terms of Sharee’ah; whereas freeing a slave is only sufficient for expiation if the freed person is Islamically proven to be a slave. Hence, if someone does not find a slave whose freeing is Islamically ordained, then he should do other valid alternatives, like feeding poor people or clothing them or fasting.
Here, it should be mentioned that the slave that should be freed as an expiation must be a Muslim as it is not sufficient to free a non-Muslim in regard to expiations according to the view of the majority of the scholars whereas Abu Haneefah took the opposite view. For more benefit, please refer to Fataawa 83687 and 84431.
Allaah Knows best.