‘Aishah narrated that the wives of the Prophet (peace and blessings of Allah be upon him) used to go out at night to al-Manasi’ (well known places in the direction of al-Baqi’) to relieve themselves and ‘Umar used to say to the Prophet (peace and blessings of Allah be upon him), “Let your wives be veiled.” But the Messenger of Allah (peace and blessings of Allah be upon him) did not do that. Then one night Sawdah bint Zam’ah, the wife of the Prophet (peace and blessings of Allah be upon him), went out at ‘Isha time and she was a tall woman. ‘Umar called out to her: “We have recognized you, O Sawdah!” hoping that hijab would be revealed, then Allah revealed the verse of hijab. (Narrated by al-Bukhari, 146; Muslim, 2170)
“O Prophet! Tell your wives and your daughters and the women of the believers to draw their cloaks (veils) all over their bodies . That will be better, that they should be known (as free respectable women) so as not to be annoyed. And Allah is Ever Oft-Forgiving, Most Merciful.” [al-Ahzab 33:59]
this verse is proof they didn't used to do this before the revelation of the verse therefore necessitating a verse be sent down so they wear jilbaabs and cover their entire bodies and faces
24:31
وَقُل لِّلْمُؤْمِنَـٰتِ يَغْضُضْنَ مِنْ أَبْصَـٰرِهِنَّ وَيَحْفَظْنَ فُرُوجَهُنَّ وَلَا يُبْدِينَ زِينَتَهُنَّ إِلَّا مَا ظَهَرَ مِنْهَا ۖ وَلْيَضْرِبْنَ بِخُمُرِهِنَّ عَلَىٰ جُيُوبِهِنَّ ۖ وَلَا يُبْدِينَ زِينَتَهُنَّ إِلَّا لِبُعُولَتِهِنَّ أَوْ ءَابَآئِهِنَّ أَوْ ءَابَآءِ بُعُولَتِهِنَّ أَوْ أَبْنَآئِهِنَّ أَوْ أَبْنَآءِ بُعُولَتِهِنَّ أَوْ إِخْوَٰنِهِنَّ أَوْ بَنِىٓ إِخْوَٰنِهِنَّ أَوْ بَنِىٓ أَخَوَٰتِهِنَّ أَوْ نِسَآئِهِنَّ أَوْ مَا مَلَكَتْ أَيْمَـٰنُهُنَّ أَوِ ٱلتَّـٰبِعِينَ غَيْرِ أُو۟لِى ٱلْإِرْبَةِ مِنَ ٱلرِّجَالِ أَوِ ٱلطِّفْلِ ٱلَّذِينَ لَمْ يَظْهَرُوا۟ عَلَىٰ عَوْرَٰتِ ٱلنِّسَآءِ ۖ وَلَا يَضْرِبْنَ بِأَرْجُلِهِنَّ لِيُعْلَمَ مَا يُخْفِينَ مِن زِينَتِهِنَّ ۚ وَتُوبُوٓا۟ إِلَى ٱللَّهِ جَمِيعًا أَيُّهَ ٱلْمُؤْمِنُونَ لَعَلَّكُمْ تُفْلِحُونَ ٣١
And tell the believing women to lower their gaze and guard their chastity, and not to reveal their adornments except what normally appears. Let them draw their veils over their chests, and not reveal their ˹hidden˺ adornments except to their husbands, their fathers, their fathers-in-law, their sons, their stepsons, their brothers, their brothers’ sons or sisters’ sons, their fellow women, those ˹bondwomen˺ in their possession, male attendants with no desire, or children who are still unaware of women’s nakedness. Let them not stomp their feet, drawing attention to their hidden adornments. Turn to Allah in repentance all together, O believers, so that you may be successful.
— Dr. Mustafa Khattab, the Clear Quran
this verse is also proof they didn't cover up completely their necks and chests before revelation of the ayah