Bulugh al-Maram 8 Marriage كتاب النكاح 12

وَعَنِ ابْنِ عُمَرَ – رَضِيَ اَللَّهُ عَنْهُمَا- قَالَ : قَالَ رَسُولُ اَللَّهِ – صلى الله عليه وسلم -{ لَا يَخْطُبْ بَعْضُكُمْ عَلَى خِطْبَةِ أَخِيهِ , حَتَّى يَتْرُكَ اَلْخَاطِبُ قَبْلَهُ , أَوْ يَأْذَنَ لَهُ اَلْخَاطِبُ } مُتَّفَقٌ عَلَيْهِ , وَاللَّفْظُ لِلْبُخَارِيِّ 1 . 1 – صحيح . رواه البخاري ( 5142 ) ، ومسلم ( 1412 ).

Narrated Ibn ‘Umar (RA): Allah’s Messenger (صلى الله عليه وسلم) said: “No one of you should ask a woman in marriage when his brother has done so already, until the one who has proposed (to her) before him gives her up, or gives him permission.” [Agreed upon. The wording is al-Bukhari’s].