Mahr as working for the father-in-law for a certain period

Q 3: I am poor and cannot afford marriage. A man offered to give me his daughter in marriage provided that I work for him for a one month period, and this shall be her Mahr (dowry to a bride from the groom). (Part No. 19; Page No. 43) The man's daughter agreed to this offer, is this permissible in Islam? Could this be a valid marriage?

A: If the matter is as mentioned, it is permissible to work for this man for one month and consider this the Mahr for his daughter; and the marriage would be valid. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.