Sunan An-Nasa'i - سنن النسائي
26. The Book of Marriage - كتاب النكاح
20) Chapter: Prohibition of Proposing Marriage To A Woman When Someone Else Has Already Proposed To Her
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."
20) باب النَّهْىِ أَنْ يَخْطُبَ الرَّجُلُ عَلَى خِطْبَةِ أَخِيهِ .
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 "