"None of you should propose marriage to a woman when someone else has already proposed to her, unless he marries (and he gives up the idea), or gives him permission."  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لاَ يَخْطُبْ أَحَدُكُمْ عَلَى خِطْبَةِ أَخِيهِ حَتَّى يَنْكِحَ أَوْ يَتْرُكَ  

[Machine] The Messenger of Allah ﷺ forbade that riders be received or gifts be sold, and that one of you proposes marriage to his brother's betrothed until the marriage is consummated or abandoned. And there should be no prayer after Asr until the sun sets, and no prayer after Fajr until the sun rises or a little after.  

نَهَى رَسُولُ اللهِ ﷺ أَنْ يُتَلَقَّى الرُّكْبَانُ أَوْ يَبِيعَ حَاضِرٌ لِبَادٍ وَلَا يَخْطُبْ أَحَدُكُمْ عَلَى خِطْبَةِ أَخِيهِ حَتَّى يَنْكِحَ أَوْ يَدَعَ وَلَا صَلَاةَ بَعْدَ الْعَصْرِ حَتَّى تَغِيبَ الشَّمْسُ وَلَا بَعْدَ الصُّبْحِ حَتَّى تَرْتَفِعَ الشَّمْسُ أَوْ تَضْحَى  

The Prophet ﷺ said: One of you must not ask a woman in marriage when his brother has done so already, and one of you must not sell (his own goods) when his brother has already sold (his goods) except with his permission. (Using translation from Abū Dāʾūd 2081)   

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ «لَا يَخْطُبُ أَحَدُكُمْ عَلَى خِطْبَةِ أَخِيهِ وَلَا يَبِيعُ عَلَى بَيْعِ أَخِيهِ حَتَّى يَأْذَنَ لَهُ»  

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." (Using translation from Nasāʾī 3240)   

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ «لَا يَخْطُبْ أَحَدُكُمْ عَلَى خِطْبَةِ أَخِيهِ»  

"لاَ تَلَقَّوُا الأجْلاَبَ، وَلاَ يَبعْ حَاضِرٌ لِبَادٍ، وَلاَ يَخْطُبْ أَحَدُكُمْ عَلَى خِطْبَةِ أَخِيهِ حَتَّى يَنْكِحَ أَوْ يَدَعَ".  

"لَا يَخْطُب أَحَدُكُمْ عَلَى خِطْبَةِ أَخِيهِ حَتَّى يَنْكِحَ أَوْ يَتْرُكَ".