Sahih
Muslim
صحيح مسلم
16
The Book of Marriage
كتاب النكاح
Chapter 6: The prohibition of proposing marriage when one's brother has already proposed, unless he gives permission or gives up the idea
باب تَحْرِيمِ الْخِطْبَةِ عَلَى خِطْبَةِ أَخِيهِ حَتَّى يَأْذَنَ أَوْ يَتْرُكَ
Sahih Muslim 1412 d
A hadith like this has been reported on the authority of Nafi' with the same chain of transmitters.
وَحَدَّثَنِيهِ أَبُو كَامِلٍ الْجَحْدَرِيُّ، حَدَّثَنَا حَمَّادٌ، حَدَّثَنَا أَيُّوبُ، عَنْ نَافِعٍ، بِهَذَا الإِسْنَادِ.
Grade: Sahih