Question: My sister is planning to go for Hajj this year, Insha Allâh, with her husband. Can I go with them, as I have no other Mahram?
Fatwa: All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The husband of a woman is not a Mahram to her sister. So, she should not travel with him even with the presence of the sister. As for the traveling of a woman who wants to perform Hajj and who could not find a Mahram, it is not a settled matter among the scholars of Islam. The majority of the Muslim scholars are of the opinion that it is not mandatory on the woman who does not find a Mahram to accompany her on Hajj trip to perform Hajj.
However, the Shafi and others believe that it is lawful for the woman who cannot find a Mahram to go on Hajj provided she finds a trustful company that will not harm her. This is also the opinion of Imam Ibn Taymiyah . We also believe that it is the most correct opinion. So, we think that you can go on Hajj with your sister and her husband provided this Hajj is your first Hajj, i.e. the mandatory Hajj and provided the company with which you will be traveling is a trustworthy one.
Allah Knows best.