I heard the Messenger of Allah ﷺ say from the pulpit, "The sons of Hisham bin Mughira have asked my permission to marry their daughter to Ali bin Abu Talib. I will not give permission, then I will not give permission, then I will not give permission, unless Ibn Abu Talib wishes to divorce my daughter and marry their daughter. She is but a part of me. What troubles her troubles me, and what harms her harms me."
سمعت رسول الله ﷺ يقول وهو على المنبر: إن بني هشام بن المغيرة استأذنوا في أن ينكحوا ابنتهم علي بن أبي طالب، فلا آذن، ثم لا آذن، ثم لا آذن إلا أن يريد ابن أبي طالب أن يطلق ابنتي، وينكح ابنتهم؛ فإنما هي بضعة مني، يريبني ما أرابها ويؤذيني ما آذاها.
Bukhari related it in the Book of Marriage (5230), and Muslim in the Book of Virtues (2249:93), both from the hadith of Layth bin Saad, from Ibn Abu Mulayka, from Miswar bin Makhrama, who mentioned it as stated.His words, "their daughter" refers to the daughter of Abu Jahl, who was Amr bin Hisham bin Mughira, the enemy of Allah and His Messenger. His two brothers, Harith bin Hisham and Salama bin Hisham, embraced Islam in the year of the conquest, and their Islam was good.Ibn Tin said, "The most correct explanation of this account is that the Prophet ﷺ forbade Ali from combining his own daughter with the daughter of Abu Jahl in marriage, because he gave as the reason that this would cause him distress, and causing him distress is forbidden by unanimous agreement. The meaning of his saying, 'I do not forbid what is lawful,' is that she would be lawful for him if Fatimah were not already his wife."There are other opinions on this matter, see Fath al-Bari (9/329).