Praise be to Allah.
A woman’s ‘awrah before her mahrams such as her father, brother, and brother’s son is her entire body except that which ordinarily appears such as the face, hair, neck, forearms and feet. Allaah says (interpretation of the meaning):
“and not to reveal their adornment except to their husbands, or their fathers, or their husband’s fathers, or their sons, or their husband’s sons, or their brothers or their brother’s sons, or their sister’s sons, or their (Muslim) women (i.e. their sisters in Islâm)”
So Allaah has permitted a woman to show her adornment before her husband and her mahrams. What is meant by adornments is the places where adornments are worn, so the site of the ring is the hand, the site of the bracelet is the forearm, the site of the earring is the ear, the site of the necklace is the neck and chest, and the site of the anklet is the calf.
Abu Bakr al-Jasaas said in his Tafseer: The apparent meaning indicates that it is permissible to show one’s adornments to the husband and those who are mentioned alongside him, such as the father and others. It is well known that what is meant is the places where adornments are worn, which are the face, hand and forearm. … This implies that it is permissible for those mentioned in the verse to look at these places, which are the sites of concealed adornment, because at the beginning of the verse it states that non-mahrams are allowed only to see the external adornment, and it is permissible for the husband and mahrams to see the hidden adornments. It was narrated from Ibn Mas’ood and al-Zubayr (that it refers to) earrings, necklaces, bracelets and anklets.
The husband and those who are mentioned alongside him are equal with regard to that. The general meaning indicates that it is permissible for those mentioned to look at the places where adornment is worn, just as it indicates that it is permissible for the husband to do so. Because Allaah mentioned alongside the father other mahrams to whom it is permanently forbidden to marry her, this indicates that those to whom the same prohibition applies come under the same ruling, such as the daughter’s husband, wife’s mother, women who are mahrams due to breastfeeding, and so on. End quote.
Al-Baghawi (may Allaah have mercy on him) said: The words of Allaah, “and not to reveal their adornment” mean that they should not uncover their adornments before non-mahrams. What is referred to here is hidden adornments. There are two types of adornment, apparent and hidden. The hidden adornments include things such as the anklets, henna on the feet, bracelets on the wrist, earrings and necklaces. It is not permissible for her to show them or for a non-mahram to look at them. What is meant by adornment is the site where the adornment is worn. End quote.
It says in Kashshaaf al-Qinaa’ (5/11): A man may look at the face, neck, hand, foot, head and calf of a mahram. Al-Qaadi said, based on this report: It is permissible (to look at) that which ordinarily appears such as the head and hands up to the elbows. End quote.
These mahrams may vary with regard to closeness and being free of fitnah. Hence a woman may show before her father that which she should not show before her husband’s son. Al-Qurtubi (may Allaah have mercy on him) said: Because Allaah mentioned husbands first and then mahrams, and stated that they were equal with regard to showing adornment, but their status varies according to human nature. No doubt uncovering before a father or brother is safer than uncovering before her husband’s son, so they vary in what may be uncovered before them, and one may show to the father what one may not show to the husband’s son. End quote.
Based on this, the woman must cover her breasts when she wants to breastfeed her son in the presence of any of her mahrams, so she may offer her child the breast beneath a blanket and the like. This is part of modesty and keenness to remain covered.
For more information please see the answer to question no. 34745.
And Allaah knows best.