The ruling on a woman traveling with her sister's husband for Hajj

This message also concerns Hajj. Sa'd Zayd al-Shami, from Thaqibah, Eastern Province. He says: I performed Hajj with my wife, and my wife suggested that her sister go with us for Hajj. I wanted to refuse because her sister is not a mahram (a relative one may not marry) to me, but I feared that my wife might think I do not want her sister to perform Hajj with us. Please inform us of the ruling on my wife's sister traveling with us, and what is the ruling on her Hajj? Does it suffice for the Hajj of Islam? May Allah reward you with good.
Answer: The answer, O questioner: There is no doubt that a woman traveling without a mahram is not permissible. It is authentically reported from the Messenger of Allah (peace and blessings be upon him) that he said: Therefore, it is obligatory for Muslims to obey the command of Allah and the command of His Messenger (peace and blessings be upon him). It is not permissible for a woman to travel for Hajj or for anything else except with a mahram, who is her brother, or her paternal uncle, or her father, or her husband. The wife's sister is not a mahram to you; you are not a mahram to her. Therefore, she is not allowed to travel with you. Even if her sister gets angry, she is not allowed to travel with you, whether for Hajj or for anything else. You may excuse yourself by citing the religious ruling and say: "It is not permissible for me to let you travel with us, and you are not a mahram to me." This is what is obligatory for you. And she must be satisfied with the command of Allah and the ruling of Allah (Glorified and Exalted is He). However, if she performed Hajj without a mahram, her Hajj is valid. She must repent and seek forgiveness from Allah for the sin she committed, and her Hajj is valid because it was performed in its proper place. But the means to it was not permissible, so she must repent to Allah for that and seek His forgiveness, and her Hajj is valid.