Is expiation obligatory upon my mother who swore an oath that her son is not her son if he does such and such, and her son, who is nine years old, did it, knowing that the oath was made hastily and without thought?

To fulfill an oath made by one who swore it is a right of a Muslim upon his brother, and this right is further emphasized for parents. If the mother swore an oath, intending it and determined to uphold it, then she must offer expiation for breaking her oath due to her son's action. The expiation is to feed ten poor persons, or clothe them, or free a slave. If she cannot find any of these, then she must fast for three days. However, if the oath was not intended, it falls under the category of a vain oath (laghw al-yameen), for which there is no expiation. The mother's statement, "You are not my son," has no consequence, and the brother is not held accountable as long as he has not reached the age of accountability.