What is the ruling on gheelah in Islam?
Question

                What is the ruling on gheelah in Islam?.
Praise be to Allah.It was said that gheelah 
    means having intercourse with a wife who is breastfeeding, or it was said 
    that it means a pregnant woman breastfeeding her child. 

    It is reported in Saheeh Muslim (1442) that the 
    Messenger of Allaah  (peace and blessings of Allaah be upon him) said: 
    “I had thought of forbidding gheelah, then I remembered that the Romans and 
    Persians do that and it does not harm their children.” 

    Al-Nawawi said: 

    The scholars differed as to what is meant by gheelah in this 
    hadeeth. Maalik said in al-Muwatta’, and al-Asma’i and other scholars 
    of Arabic language said that it means having intercourse with a woman who is 
    breastfeeding. Ibn al-Sakeet said: It means a woman breastfeeding when she 
    is pregnant. 

    The scholars said: The reason why the Prophet  (peace and 
    blessings of Allaah be upon him) thought of forbidding it was that he feared 
    that the breastfed child may be harmed by it. The doctors used to say that 
    that milk was harmful, and the Arabs disliked it and feared it. 
The hadeeth shows that 
    gheelah is permissible, because the Prophet  (peace and blessings of 
    Allaah be upon him) did not forbid it, and he stated the reason why he did 
    not forbid it. 

    Sharh Muslim, 10/17, 18 

    Muslim (1443) narrated from Sa’d ibn Abi Waqqaas that a man 
    came to the Messenger of Allaah  (peace and blessings of Allaah be upon 
    him) and said: “I practice coitus interruptus (‘azl) with my wife.” The 
    Messenger of Allaah  (peace and blessings of Allaah be upon him) said to 
    him: “Why do you do that?” The man said: “Out of compassion towards her 
    child.” The Messenger of Allaah  (peace and blessings of Allaah be upon 
    him) said: “If that was harmful, it would have harmed the Persians and 
    Romans.” 

    There is nothing that is contrary to this permission except a 
    weak hadeeth that was narrated by Abu Dawood (3881) and Ibn Maajah (2012) 
    from Asma’ bint Yazeed (may Allaah be pleased with her), according to which 
    the Prophet  (peace and blessings of Allaah be upon him) forbade 
    gheelah. This hadeeth was classed as da’eef by Shaykh al-Albaani in 
    Da’eef Sunan Abi Dawood. 

    Ibn al-Qayyim (may Allaah have mercy on him) quoted in 
    Tahdheeb al-Sunan the ahaadeeth which indicate that it is permitted, 
    then he said: “These ahaadeeth are more sound than the hadeeth of Asma’ bint 
    Yazeed. Even if her hadeeth is proven to be saheeh, it may be understood as 
    referring to that which is preferable, not as meaning that it is haraam. End 
    quote. 

    He also said in Zaad al-Ma’aad (5/147, 148): 
There is no doubt that 
    having intercourse with a breastfeeding woman is something that is 
    widespread, and it is too hard for a man to keep away from his wife for the 
    duration of the breastfeeding period. If having intercourse with 
    breastfeeding women was haraam, it would be well known in the religion, and 
    the ummah and the best of generations would have known that. But there is no 
    clear report that any of them regarded it as haraam. It is known that the 
    hadeeth of Asma’ is to be regarded as advice about what is better for the 
    child and to avoid interrupting the child’s milk supply in the event of the 
    mother becoming pregnant.  

    Conclusion: gheelah is not haraam or makrooh, because there 
    is no proof that the Prophet  (peace and blessings of Allaah be upon 
    him) forbade it. The one who avoids it in order to be on the safe side for 
    his child is not doing anything wrong. 

    And Allaah knows best.