Does the fact that the wives of the Prophet, may Allah bless him and grant him peace, performed Hajj more than once after his death indicate the permissibility for a woman to perform Hajj without a mahram, but with a group of women accompanied by their mahrams?

The preponderant view among scholars is that it is not permissible for a woman to travel for Hajj or anything else without a mahram, based on the Prophet's (peace be upon him) saying: "A woman should not travel except with a mahram." As for the argument made concerning the Hajj performed by the Mothers of the Believers without a mahram, the response is that the hadith does not negate the presence of their mahrams, and that the sending of Uthman and Abd al-Rahman ibn Awf was for added honor and reassurance. Even if it were assumed that there was no mahram, it would be an ijtihad (independent reasoning) that does not contradict the explicit text. As for the opinion of those who restrict this to the Mothers of the Believers because they are mahram to all men, this is not accepted; because their mahramiyyah (status of being a mahram) relates to prohibition (of marriage) not to being a mahram (in the sense of accompanying for travel).