Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.044.
Section : Wearing a Short Underpants (short underwear).
Sa’id ibn Mansur reported from ‘Aishah that she held that a muhrim may wear underpants. Al Hafiz remarked: “This is an opinion of ‘Aishah, but the majority of scholars hold wearing underpants is forbidden for a muhrim, because it is similar to wearing trousers which are forbidden for a muhrim.” (Bukhari)