Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Thanks for your question, and we ask Allah Almighty to help us seek what is lawful and avoid what is discouraged and prohibited in all our actions.
Every Muslim is strongly recommended to follow the Prophetic guidance in enjoying the intimate relationship with his wife. The female breast milk is intended for babies, and hence it should be left for them. It is not for adult consumption.
With this in mind, we can say that the husband is allowed to suck on it gently, but he is not allowed to draw the milk in. According to the opinion of some scholars, if he were to do so, it could endanger the marriage relationship—if suckling is done five times.
Responding to the question, the Islamic Religious Council of Singapore, states the following:
The drinking of your wife’s milk does not invalidate your marriage. The husband and wife are still considered as a legal couple in the eyes of the Shari`ah. This is because only a child who has suckled a woman’s milk fully, more than five times, is considered as the woman’s suckled child.
Hence, your children are considered as both your legitimate children and you can continue your normal relationship as husband and wife.
Almighty Allah knows best.