Vowing to return the daughter back to her mother after visiting him but failing to fulfill the vow

Q: A friend of mine married a woman and they had a daughter. He later divorced her and their daughter lived with her mother until she was 16. In 1420 A.H., my friend asked me to mediate with his ex-wife to ask if his daughter could come to stay with him in his house in Jeddah. He could not ask himself, because he had not given her any Nafaqah (obligatory financial support) during the time she had been with her mother. He wanted his daughter to stay with him for a month during the summer holidays, after which he would return her to her mother. I went to talk to the girl’s mother about this and she asked me to promise her that her daughter would return after the month. I contacted the girl’s father and told him this. He said to me, "I promise you by Allah, that I will return her (Part No. 23; Page No. 315) to her mother, even if she is dead." On that, I gave the girl’s mother an oath by Allah, based on his promise to me. Sadly, after the month, the girl’s father refused to return the girl to her mother, who was suffering from a heart disease and later died in hospital in the month of Dhul-Hijjah, 1420 A.H. The girl is still living with her father.My question to Your Eminence is:1. What should I do as I gave my oath and did not fulfill it, as it was not in my power to do so? I did try my best with the girl’s father, without success as he did not respond to me.2. I have broken off all relations with the girl’s father and we no longer exchange phone calls or visits, as he broke his agreement with me. Am I sinful for doing this, bearing in mind that he is not a relative of mine?I hope that you will advise me on this matter and tell me what I should do in regard to this. May Allah bless you for it!

A: It is obligatory on you to offer the Kaffarah (expiation) for breaking an oath, which is feeding ten needy people, giving each of them 1.5 kg of food, or clothing ten needy people, giving each of them one garment, or freeing a believing slave. If you cannot do this, it is obligatory on you to perform Sawm (Fasting) for three days. (Part No. 23; Page No. 316) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.