Shaikh ِAbdul Azeez Aal Ash Shaikh was asked:
This is a question from a sister and it is repeated a lot regarding the shoulder Abaya. Is it lawful if it is plain and not designed with anything beautiful?
The Shaikh answered:
The most important thing is for the woman to cover her body (completely) when she leaves the house. And the Abaya being decorated it can lead to others looking at her. Therefore her distancing herself from beautification is from covering the woman …
Fatawa ‘Ala Hawaa: 1434-06-26. From the 10 minute mark to 10:32