Can a vow made to Allah be divided, or must it be fulfilled all at once as stated in the vow?

Vowing to donate someone else's money, such as a mother vowing to give her son's money in charity, falls under the category of "vowing what one does not possess." The Prophet, peace and blessings be upon him, said: "There is no vow upon the son of Adam concerning what he does not possess." This means that such a vow is invalid, non-binding, and holds no legal weight. If someone makes a vow concerning something owned by another, neither the owner nor the person who made the vow is bound by it, because this vow is void and has no effect.

Scholars differ on whether an expiation for a broken oath (kaffarat yameen) is obligatory for this type of vow. The majority do not consider it obligatory, citing the hadith: "There is no vow in disobedience, nor concerning what a servant does not possess." In conclusion, the vow your mother made is not binding, and nothing is required as a result. However, as a precautionary measure, it is preferable to offer an expiation for a broken oath, out of deference to those scholars who have deemed it obligatory.