What was the attire of a Muslim woman before the فرض (imposition) of hijab, and did any women remain unveiled after the revelation of the verses of hijab, and how did the Prophet, peace and blessings be upon him, deal with them, and is disobeying hijab a minor or major sin?

Before the obligation of Hijab, the Muslim woman's attire did not include the full Shar'i Hijab, but they wore modest clothing that reflected chastity and honor. The Prophet, peace and blessings be upon him, encouraged noble character and chastity from the beginning of his call.

After its obligation, the believing women hastened to adhere to it voluntarily. No display of adornment (tabarruj) was recorded from them; rather, they submitted to the command of Allah and His Messenger, as narrated in the hadith of Aisha and Umm Salama.

As for the hypocrite women, they showed outward adherence, but no display of adornment was known from the women of hypocrisy in that pure era.

Abandoning Hijab and displaying adornment (tabarruj) is a grave sin. The Prophet, peace and blessings be upon him, warned women who display adornment with Hellfire and described them as a type of people of Hell who will not enter Paradise nor find its scent. It was also reported that the worst of women are those who display adornment and imagine themselves [to be virtuous], and they are the hypocrite women, and only a few of them will enter Paradise.