We have previously discussed what it is permissible for a woman to show in front of her mahrams and in front of other women. See the answer to question no. 113287, 82994, 34745 and 115351. To sum up, she should not uncover in front of women anything but that which ordinarily appears.
With regard to uncovering the breast in order to feed her child, the scholars granted a concession allowing that because there is a need for it.
Shaykh Ibn Uthaymeen (may Allah have mercy on him) said:
We must understand that there is a difference between saying What is awrah? and What is the clothing that it is prescribed for a woman to wear? so that there will be no confusion between the two matters.
The clothing that is prescribed for a woman to wear in front of mahrams is that which covers all of her body apart from the head, hands and feet. This is what is prescribed.
With regard to the issue of awrah, the awrah for a woman in front of other women is like the awrah for a man in front of other men, i.e., the area between the navel and the knee. But saying that does not mean that it is permissible for a woman to appear in front of other women wearing nothing but pants that cover from the navel to the knee. No one would say that. Whoever says such a thing is misguided. Rather what is meant is that if a woman is wearing covering clothes, and she needs to uncover her forearms to do some work or because of some disease in the forearms and like, or she wants to breastfeed her child in front of other women, so she uncovers her breast in front of the women, there is nothing wrong with that.
So there is a difference between the concept of awrah and the manner of dress that is prescribed. What is prescribed for women is that their clothing should cover them properly, and it is permissible for a woman to uncover her head, face, neck and hands, and even her forearms, feet and lower legs in front of her mahrams. But that does not mean that we say she can wear short dresses in front of her mahrams; not at all.
This is another matter. But if we assume, for example, that she lifts up her dress for some reason, and her mahrams are present and her lower leg shows, then there is nothing wrong with that.
End quote from al-Liqa' al-Maftooh. 126/23. See also al-Liqa' al-Maftooh, 31/17
Based on that:
If you need to breastfeed your child in the presence of other women, there is nothing wrong with that, but you have to try to remain covered as much as possible, by covering whatever you can cover when breastfeeding.
If you can go off to one side away from them, or go into another room, that is preferable, because it is part of modesty, dignity and remaining covered.
With regard to children, you should avoid breastfeeding in front of those who have reached the age of discernment and who know what the awrah is.
The righteous woman should be a teacher and an example for her sisters, so as to spread goodness and decency.
We ask Allah to guide you and help you.
And Allah knows best.
Reproduced from Islam QA