Praise be to Allah, the Lord of the Worlds.
Jurists of the four schools of thought are agreed that the face is the front part of a person`s head. In width, it is the area between the two ears. In length, it is the area extending from the forehead where the hair roots begin to the lower chin. For further details on the limits of the face from an Islamic perspective, kindly refer to {Moghni Al-Mohtaj, 1/175}.
Moreover, the Maliki, Shafie, and Hanbali schools are agreed that a woman must cover all her body during prayer to the exception of the face and hands, and the Hanafi school has agreed with them on the limits of a woman`s face during prayer. Accordingly, the aforementioned shows the limit of a woman`s face allowed to be uncovered.
This means that the area referred to in the above question isn`t considered part of the face according to the above definition. Therefore, it is impermissible for a woman to uncover it, be that during or outside prayer. Rather, that area must be covered. Ibn Atyah, a Maliki scholar, has granted a concession for whatever appears of a woman`s face due to a necessary movement. He based this on his interpretation of the verse, "and to display of their adornment only that which is apparent"{An-Nour, 31}. It is stated in {Tafseeer Ibn Atyah, 4/178}, "This verse indicates that a woman is commanded not to display any part of her Awrah and to hide every adornment, and whatever appeared due to a necessary movement is pardoned." In addition, scholars have permitted the appearance of a little part of a woman`s Awrah during prayer.
Ibn Mifleh, a Hanbali Imam, stated, "A woman`s prayer isn`t invalidated by the appearance of a little part of her Awrah, and even if she did so intentionally, according to some scholars."{Al-Forou` Wa Tas-heeh Al-Forou`, 2/39}.
In conclusion, a woman must be keen on not revealing any part of the area between her neck and lower chin. However, if any part of that area was revealed during prayer, the prayer remains valid, and if the same happened outside prayer, then that is pardoned or else responsible Muslim women will be caused harm and faced with although Almighty Allah says, "and hath not laid upon you in religion any hardship;"{Al-Hajj, 78}. In addition, there is a Sharia rule, in this regard, which states, "Difficulty demands facilitation." And Allah the Almighty knows the best. Note by translator: According to Fuqaha`, everything that is haram for a man and a woman to uncover is Awrah.