Sahih al-Bukhari 5142
صحيح البخاري#5142Sahihحَدَّثَنَا مَكِّيُّ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا ابْنُ جُرَيْجٍ، قَالَ سَمِعْتُ نَافِعًا، يُحَدِّثُ أَنَّ ابْنَ عُمَرَ ـ رضى الله عنهما ـ كَانَ يَقُولُ نَهَى النَّبِيُّ صلى الله عليه وسلم أَنْ يَبِيعَ بَعْضُكُمْ عَلَى بَيْعِ بَعْضٍ، وَلاَ يَخْطُبَ الرَّجُلُ عَلَى خِطْبَةِ أَخِيهِ، حَتَّى يَتْرُكَ الْخَاطِبُ قَبْلَهُ، أَوْ يَأْذَنَ لَهُ الْخَاطِبُ.
Narrated Ibn `Umar:The Prophet (ﷺ) decreed that one should not try to cancel a bargain already agreed upon between some other persons (by offering a bigger price). And a man should not ask for the hand of a girl who is already engaged to his Muslim brother, unless the first suitor gives her up, or allows him to ask for her hand
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 67:78