1,001 Sayings and Deeds of the Prophet
God’s Messenger believed that a woman who suckled an adult male who was not a close relation made marriage not only impossible for him but undesirable, he became the equivalent of a close relation and therefore could spend time with her alone.
Aisha (Allah be pleased with her) reported that Salim, the freed slave of Abu Hadhaifa, lived with him and his family in their house. She (i. e. the daughter of Suhail came to Allah's Apostle (may peace be upon him) and said: Salim has attained (puberty) as men attain, and he understands what they understand, and he enters our house freely, I, however, perceive that something (rankles) in the heart of Abu Hudhaifa, whereupon Allah's Apostle (may peace be upon him) said to her: Suckle him and you would become unlawful for him, and (the rankling) which Abu Hudhaifa feels in his heart will disappear.
She returned and said: So I suckled him, and what (was there) in the heart of Abu Hudhaifa disappeared.
Sahih Muslim 8:3425
If a female was suckled by the wife of a man, any man it would seem, it made that man her relation and that man’s brothers her uncles, for the breast milk she got was the “brother’s milk” even if it was his wife’s milk on which she nursed.
Aflah asked the permission to visit me but I did not allow him. He said, "Do you veil yourself before me although I am your uncle?"
Aisha said, "How is that?"
Aflah replied, "You were suckled by my brother's wife with my brother's milk."
I asked Allah's Apostle about it, and he said, "Aflah is right, so permit him to visit you."
It’s complicated I know, so here is a variation which may make it easier to understand.
That while Allah's Apostle was with her, she heard a voice of a man asking permission to enter the house of Hafsa.
Aisha added: I said, "O Allah's Apostle! This man is asking permission to enter your house."
The Prophet said, "I think he is so-and-so," naming the foster-uncle of Hafsa.
Aisha said, "If so-and-so, 'naming her foster uncle', were living, could he enter upon me?"
The Prophet said, "Yes, for foster suckling relations make all those things unlawful which are unlawful through corresponding birth (blood) relations."
The witty and bold Aisha was not afraid to use sarcasm which her husband may not have appreciated to let him know when she thought he was spouting nonsense.
My foster uncle came and asked permission (to enter) but I refused to admit him till I asked Allah's Apostle about that. He said, "He is your uncle, so allow him to come in."
I said, "O Allah's Apostle! I have been suckled by a woman and not by a man."
Allah's Apostle said, "He is your uncle, so let him enter upon you."
Having been made unlawful to marry i.e. Muhrim by sulking milk meant for an infant, did not mean you could now just drop in on the woman's whose breasts you had cupped and supped on, dressed and perfumed anyway you like.
Narrated Ibn Umar:
A person asked Allah's Apostle, "What should a Muhrim wear?"
He replied, "He should not wear shirts, trousers, a burnus (a hooded cloak), or clothes which are stained with saffron or Wars (a kind of perfume). Whoever does not find a sandal to wear can wear Khuffs, but these should be cut short so as not to cover the ankles"
A foster brother could spend time alone with the daughter of the parents who raised him if he had been suckled while in their care before the age of two.
Once the Prophet came to me while a man was in my house. He said, "O Aisha! Who is this (man)?"
I replied, "My foster brothers"
He said, "O Aisha! Be sure about your foster brothers, as fostership is only valid if it takes place in the suckling period (before two years of age)."
Breast milk could sour a marriage:
Narrated Abdullah bin Abu Mulaika from 'Uqba bin Al-Harith:
Uqba married the daughter of Abu Ihab bin Aziz, and then a woman came and said, "I suckled 'Uqba and his wife."
Uqba said to her, "I do not know that you have suckled me, and you did not inform me."
He then sent someone to the house of Abu Ihab to enquire about that but they did not know that she had suckled their daughter.
Then Uqba went to the Prophet in Medina and asked him about it.
The Prophet said to him, "How (can you keep your wife) after it has been said (that both of you were suckled by the same woman)?"
So, he divorced her and she was married to another (husband).
The woman who soured Uqba’s marriage was a” black lady”.
Narrated 'Uqba bin Al-Harith:
I married a woman and then a black lady came to us and said, "I have suckled you both (you and your wife)."
So I came to the Prophet and said, "I married so-and-so and then a black lady came to us and said to me, 'I have suckled both of you.' But I think she is a liar."
The Prophet turned his face away from me and I moved to face his face, and said, "She is a liar."
The Prophet said, "How (can you keep her as your wife) when that lady has said that she has suckled both of you? So abandon (i.e., divorce) her (your wife)."
There is no mention in the hadiths of Bukhari as to whether this had any effect on the complexion of Uqba’s, or that of his soon-to-be-divorced wife’s skin, as could have been expected considering the powers the Prophet attributed to breast milk.