The Book of Marriage
16/6. Chapter:
The prohibition of proposing marriage when one's brother has already proposed, unless he gives permission or gives up the idea
Sahih Muslim
حَدَّثَنَا يَحْيَى بْنُ أَيُّوبَ، وَقُتَيْبَةُ، وَابْنُ، حُجْرٍ جَمِيعًا عَنْ إِسْمَاعِيلَ بْنِ جَعْفَرٍ، - قَالَ ابْنُ أَيُّوبَ حَدَّثَنَا إِسْمَاعِيلُ، - أَخْبَرَنِي الْعَلاَءُ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " لاَ يَسُمِ الْمُسْلِمُ عَلَى سَوْمِ أَخِيهِ وَلاَ يَخْطُبْ عَلَى خِطْبَتِهِ " .
Abu Huraira (Allah be pleased with him) reported Allah's Messenger (ﷺ) as saying: The Muslim should not purchase in opposition to his brother, and he should not make the proposal of marriage on the proposal already made by his brother.
Reference : Sahih Muslim 1413dIn-book reference : Book 16, Hadith 64USC-MSA web (English) reference : Book 8, Hadith 3292