وَعَنِ ابْنِ عُمَرَ رَضِيَ اَللَّهُ عَنْهُمَا
قَالَ: قَالَ رَسُولُ اَللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ -«لَا يَخْطُبْ بَعْضُكُمْ عَلَى خِطْبَةِ أَخِيهِ، حَتَّى يَتْرُكَ اَلْخَاطِبُ قَبْلَهُ، أَوْ يَأْذَنَ لَهُ اَلْخَاطِبُ»
The Messenger of Allah (sallallahu alayhi wa sallam) 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.”.
Bulugh al-Maram 1134, Book 8, Marriage, Hadith 12. 1 min read