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.