If my sister and I wanted our kids, who are born a few months apart, to be siblings via breast milk, is it permissible? Are we able to do so with bottle feeding? If so, how many feeds does it need to be?

There is no Islamic issue with breastfeeding the son of a brother, a sister, or others to make them mahram (non-marriageable) to the breastfeeding woman and her children, thus making it easier for them to interact and enter her presence. Aisha (may Allah be pleased with her) used to encourage the daughters of her sisters and brothers to breastfeed anyone she wished to see and allow into her home.

This is based on the narration recorded by Abu Dawood (2061) and authenticated by Al-Albani in Sahih Abi Dawood.

There are two conditions for breastfeeding that establish the mahram relationship:

1. It should be five or more breastfeedings because of the hadeeth of ‘Aa’ishah (may Allah be pleased with her), who said: “Among the things that were revealed of the Qur’an was that ten definite breastfeedings make a person a mahram, then that was abrogated and replaced with five definite breastfeedings,” Narrated by Muslim, no. 1452.

2. That should be within the first two years of the child’s life because of what is proven by the Prophet (blessings and peace of Allah be upon him) in the hadeeth of ‘Abd-Allah ibn al-Zubayr, that the Messenger of Allah (blessings and peace of Allah be upon him) said: “There is no breastfeeding except that which fills the stomach.” Narrated by Ibn Maajah (1946)

Also Saheeh al-Jaami‘, no. 7495. al-Bukhaari (may Allah have mercy on him) said in his Saheeh: “Chapter: One who says: There is no breastfeeding after two years because Allah says (interpretation of the meaning): ‘The mothers shall give suck to their children for two whole years, (that is) for those (parents) who desire to complete the term of suckling’ [al-Baqarah 2:233]”.

Breastfeeding means that the infant takes the nipple and suckles from it, then lets it go by himself to breathe or move. Based on that, the five breastfeeding sessions may occur in one or more sittings.

If your sister’s daughter breastfed from you five times, then she has become your daughter through breastfeeding and a sister to all your children and to any other child who breastfed from you five times.

Similarly, if your son breastfed five times from his maternal aunt, she has become a mother to him through breastfeeding, and he has become a brother to all of her children and any other child who breastfed from her.

The mahram relationship is not limited to the girl and boy asked about. Rather the girl becomes a sister to all of your children, present and future, and she is a daughter to your husband and a sister to all of his children from any other wife, if applicable.

Breastfeeding that establishes a non-marriageable relationship (raḍā‘ al-muḥarrim) is not limited to directly nursing from the breast. If milk is placed in a container and consumed by the child, this is also considered valid breastfeeding according to the majority of scholars.

Ibn Qudamah (may Allah have mercy on him) said:

“Al-Shafi‘i said, ‘Feeding through sa‘ṭ or wajur is equivalent to breastfeeding.’ The meaning of sa‘ṭ is to pour milk into the nose using a container or otherwise, and wajur is to pour it directly into the throat without suckling from the breast. There is a difference of opinion regarding whether such methods establish the prohibition (taḥrīm). The most authentic view, based on the stronger narration, is that prohibition is established through such feeding, just as it is through traditional breastfeeding. This is the opinion of Al-Sha‘bi, Al-Thawri, the scholars of Aṣḥāb al-Ra’y, and Malik in relation to wajur.

The second view is that prohibition is not established through such feeding. This is the choice of Abu Bakr, the Madhhab of Dawood, and the opinion of ‘Aṭā’ al-Khurasani regarding sa‘ṭ. They argue that this is not classified as breastfeeding (raḍā‘), and Allah and His Messenger only prohibited through explicit breastfeeding.”

Evidence supporting the establishment of a prohibition (taḥrīm) through non-direct methods of breastfeeding comes from the narration of Ibn Mas‘ud (may Allah be pleased with him), who reported that the Prophet (peace and blessings be upon him) said:

“Breastfeeding does not establish prohibition except that which strengthens the bones and nourishes the flesh.”
(Reported by Abu Dawood).

This is because milk, whether consumed through suckling or other means, reaches the same place in the body, producing the same effects of nourishing the flesh and strengthening the bones as direct breastfeeding. Therefore, it should result in the same rulings regarding prohibition.

(Adapted slightly from “Al-Mughni” (8/139) by Ibn Qudamah).

The conditions for maḥramīyah (prohibition of marriage through breastfeeding) require that the breastfeeding consists of five separate feedings and that the child has not yet surpassed two years of age.

In the case of administering milk from a container, the five feedings should be provided at distinct and separate intervals.

Ibn Qudamah states in Al-Kāfi (5/65):

“If the milk is expressed into a container, whether all at once or in multiple sessions, and then fed to the child at five different intervals, it constitutes five feedings. However, if it is consumed all at once, it is counted as a single feeding, because the determining factor is the act of the child drinking. The prohibition is established by this act, so it must be measured according to whether it occurs separately or consecutively.”

This emphasizes the importance of distinct and separate acts of nursing in establishing the prohibition.