Answer
Wa `alaykum as-Salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
The son-in-law is considered a mahram (unmarriageable relative). So, he is allowed to accompany his mother-in-law in any travel.
Responding to your question, Dr. `Abdul-Fattah Edris, Professor of Usul Al-Fiqh, at Al-Azhar University, states:
Yes, a woman can take her son-in-law as a mahram in her travel for Hajj.
Also, she can accompany him in any travel, as he is considered a mahram for her forever. In the verse that enumerates the unmarriageable female relatives, Allah Almighty says, {… and the mothers of your wives…} (An-Nissa’ 4:23)
Allah Almighty knows best.
Editor’s note: This fatwa is from Ask the Scholar’s archive and was originally published at an earlier date.