What is the ruling on performing Hajj while wearing a shoulder abaya, and what is the difference between it and a head abaya, knowing that both fulfill the requirement of covering?

The ruling on whether it is permissible to wear a shoulder abaya during Hajj or not depends on the general ruling concerning its wear. There is a difference between a head abaya and a shoulder abaya; the former offers more complete coverage, while the latter might accentuate the shoulders and reveal the size of the head. This contradicts Allah's command in His saying: {They should draw over themselves some of their outer garments (jilbāb)}.

Some scholars, such as Ibn Baz, Ibn Uthaymeen, Bakr Abu Zayd, and Abdul Muhsin Al-Abbad, have ruled against wearing the shoulder abaya because it accentuates and reveals the size of the head, involves imitation of men, and leads to fitna (temptation/strife).

Nevertheless, if the lawful (shar‘i) covering is achieved with a shoulder abaya, by wearing with it a spacious headscarf (tarḥa or khimār) over the head, then there is no objection to wearing it when going out for Hajj or other occasions.