The Messenger of Allah ﷺ said, "None of you should propose marriage to a woman already proposed to by his brother, nor sell over the sale of his brother, except with his permission."
حدثنا الحسن بن علي حدثنا عبد الله بن نمير عن عبيد الله عن نافع
قال رسول الله ﷺ لا يخطب أحدكم على خطبة أخيه ولا يبع على بيع أخيه إلا بإذنه
Agreed upon [by Bukhari and Muslim]. Ahmad also reported it, 2/142, from Abdullah bin Numayr through him.Muslim narrated it in the Book of Marriage, chapter "The Prohibition of Proposing to a Woman Already Proposed to by One's Brother"... etc, hadith 1412, from the hadith of Ubaydullah.Bukhari narrated it in the Book of Marriage, chapter "A Man Should Not Propose to a Woman Already Proposed to by His Brother Until He Marries or Withdraws," hadith 5142, from the hadith of Nafi, through him.