Sunan Ibn Majah, Hadith 1868 ⓘ
It was narrated from Ibn Umar that: the Messenger of Allah said: “A man should not propose to a woman to whom his brother has already proposed.”
حَدَّثَنَا يَحْيَى بْنُ حَكِيمٍ، حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ عُبَيْدِ اللَّهِ بْنِ عُمَرَ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " لاَ يَخْطُبِ الرَّجُلُ عَلَى خِطْبَةِ أَخِيهِ " .
also referenced under: Book 9, Hadith 1941 (In-Book) & Volume 3, Book 9, Hadith 1868 (DarusSalam)