Hadith 3242
Chapter 20: Prohibition of Proposing Marriage To A Woman When Someone Else Has Already Proposed To Her - كتاب النكاح
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا غُنْدَرٌ، عَنْ هِشَامٍ، عَنْ مُحَمَّدٍ، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " لاَ يَخْطُبْ أَحَدُكُمْ عَلَى خِطْبَةِ أَخِيهِ " .
It was narrated from Abu Hurairah that the Prophet said:
"None of you should propose marriage to a woman when someone else has already proposed to her."
Reference : Sunan an-Nasa'i 3242
In-book reference : Book 26, Hadith 47