The ruling on one who swears not to enter a house and then buys it

Question: A woman swore that she would not enter her son's house after her husband's death. The mother wants to buy the house, and the son agrees. Is it permissible for the mother to buy the house and live in it? If it is not permissible, is there an expiation?

Answer: There is no harm in her buying the house if its owners permit the sale. If she enters it after buying it, she owes no expiation, because it has become her house, not her son's. If she enters her son's house where he lives, she owes an oath expiation, whether the house is owned or rented.
The oath expiation is feeding ten poor people, or clothing them, or freeing a slave. Whoever cannot find the means to do so must fast for three days, as Allah the Exalted specified in Surat al-Ma'idah.
What is given to each poor person is half a sa' (a dry measure of about 3 kg) of the local staple food, such as dates, rice, or something else. Its amount is approximately one and a half kilograms. If she feeds them breakfast or dinner, or clothes each of them with a garment that suffices for prayer, that is sufficient.
If her son is living in the house after the purchase, and she enters it before he moves out, she owes the aforementioned expiation. And success is from Allah.