Is giving charity to one's mother considered an act that removes harm and for which the doer is rewarded, or is it considered an obligation?

It is permissible to give voluntary charity to one's parents, and it is considered among the greatest acts of proximity [to Allah]; for the Prophet, peace and blessings be upon him, said: "Charity given to a poor person is one charity, and charity given to a relative is two: charity and maintaining kinship ties." So, if the father provides the mother with her basic needs, and the charity is intended to ease her burden and provide her with more comfort, then it is a good deed for which reward is hoped.