Can Husband Drink Milk of Wife in Islam?
Question

My wife is currently feeding our newborn child. During sex, I drank her milk. Is her milk halal for me?
Praise be to Allah.Rulings related to breastfeeding in Islam
Before answering this question, we must explain some important points about the rulings concerning breastfeeding .
1. Breastfeeding is proven in the Quran and Sunnah, and by ijma (scholarly consensus).
Allah says (interpretation of the meaning): 
“… your foster mothers who gave you suck, your foster milk suckling sisters…” [al-Nisa 4:23]
Ibn 'Abbas reported that the Prophet (peace and blessings of Allah be upon him) said: “What is forbidden by suckling or breastfeeding is the same as what is forbidden by nasab (lineage).” (Agreed upon; al-Bukhari, Muslim, 1444)
The scholars agree that the effect of rada’ah (breastfeeding) prohibits marriage and creates the relationship of mahram, and permits seeing and being alone (with the people to whom one is related through rada’ah).
2. For breastfeeding to have the effect of transmitting its benefits from the nursing woman to the child suckled, it must meet certain conditions, which are:
1.     The breastfeeding must happen within the first two years of the child’s life, 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]
2.     The number of breastfeedings must total the known five feeds, in which the child eats his fill as if eating and drinking. If the child leaves the breast for a reason, such as to take a breath or to switch from one breast to the other, this (i.e., each separate time the child latches on) is not counted as one breastfeeding. This is the opinion of al-Shafi'i, and the opinion favoured by Ibn al-Qayyim. 
The definition of rada’ah (one breastfeeding) is when the child sucks at the breast and drinks until the milk enters his stomach, then he leaves the breast of his own accord. 
The evidence for the number five (number of breastfeedings) is the report from ‘Aishah (may Allah be pleased with her) who said: “There was in the Quran [an ayah which stipulated that] ten [was the number of] breastfeedings which created the relationship of mahram , then this was abrogated [by another ayah which stipulated] five. The Messenger of Allah (peace and blessings of Allah be upon him) died and [the ayah which stipulated five] was still being recited as part of the Quran.” (Reported by Muslim, 1452). 
In other words, the abrogation came so late that when the Prophet (peace and blessings of Allah be upon him) died, some people had not yet heard that this ayah had been abrogated, but when they heard that it had been abrogated, they stopped reciting it, and agreed that it should not be recited, although the ruling mentioned in the ayah remained in effect. 
This is an abrogation of the recitation without abrogation of the ruling, which is one type of abrogation.
Having understood this, breastfeeding after the first two years does not create any relationship of mahram. This is the opinion of the majority of scholars, and among the references which they quote is the verse cited above, along with the hadith of the Prophet (peace and blessings of Allah be upon him): “Nothing of breastfeeding creates the relationship of mahram except what fills the stomach to bursting point, before (the age of) weaning.” Reported by al-Tirmidhi. (No. 1152), who said: This is a hasan sahih hadith. 
The application of this according to the scholars among the Companions of the Prophet (peace and blessings of Allah be upon him) and others is that breastfeeding does not create the relationship of mahram except when it is within the first two years, and anything after the first two whole years does not create any such relationship.”
There are some other reports from the Sahabah, such as that narrated from Abu ‘Atiyah al-Wadi'i, who said: “A man came to Ibn Mas’ud and said: ‘My wife was with me and her breasts were full of milk (she was engorged). I began to suck it and spit it out. Then I came to Abu Musa.’ He (Ibn Mas’ud) said, ‘What did you tell him?’ So he (Abu Musa) told him what he had told him. Then Ibn Mas’ud stood up, took the man’s hand (and said), ‘Do you think this is an infant? Breastfeeding is what produces the growth of flesh and blood.’ Abu Musa said: ‘Do not ask me anything when this scholar is among you.’” (Reported by ‘Abd al-Razzaq in al-Musannaf, 7/463, no. 13895).
In al-Muwatta (2/603), Malik reported that Ibn ‘Umar said: “There is no breastfeeding except for the one who is breastfed in infancy; there is no breastfeeding for one who is grown up.” Its isnad is sahih.
Can husband drink milk of wife in Islam?
Malik also reported in al-Muwatta that ‘Abd-Allah ibn Dinar said: “A man came to ‘Abd-Allah ibn ‘Umar when I was with him in the court-house, asking him about breastfeeding one who is grown up. ‘Abd-Allah ibn ‘Umar said: ‘A man came to ‘Umar ibn al-Khattab and said, “I have a slave-girl with whom I used to have sexual relations, and my wife went to her and gave her her milk, then when I went to her, she said, ‘Stop, by Allah I have given her my milk.’” ‘Umar said, “Punish her (your wife), and (continue to) go to your slave-girl, for (the ruling on) breastfeeding only applies to breastfeeding of infants.”’” Its isnad is sahih.
From this it is clear that drinking one’s wife’s milk has no effect and does not create the relationship of mahram. 
Ibn Qudamah said in al-Mughni (9/201): 
“One of the conditions of breastfeeding creating the relationship of mahram is that it should be within the first two years. This is the opinion of most of the scholars. Something like this was narrated from ‘Umar, ‘Ali, Ibn ‘Umar, Ibn Mas’ud, Ibn ‘Abbas, Abu Hurayrah and the wives of the Prophet (peace and blessings of Allah be upon him), apart from ‘Aishah. It was also the opinion of al-Shi’bi, Ibn Shubrumah, al-Awza’i, al-Shaafi’i, Ishaq, Abu Yusuf, Muhammad, and Abu Thawr, and was narrated in one report from Malik.
On the basis of the above, drinking one’s wife’s milk has no effect, but it is better to avoid it.
Shaykh Muhammad ibn Salih al-‘Uthaymin was asked about this matter, and he replied: 
“Breastfeeding a grown-up has no effect, because the breastfeeding which has an effect (of creating the relationship of mahram) is that which consists of five feedings or more within the first two years, before weaning. 
On this basis, if it happened that someone breastfed from his wife or drank her milk, he does not become her son.” (Fatawa Islamiyyah, 3/338)
And Allah knows best.