(6) باب تَحْرِيمِ الْخِطْبَةِ عَلَى خِطْبَةِ أَخِيهِ حَتَّى يَأْذَنَ أَوْ يَتْرُكَ
Ibn Umar (Allah be pleased with them) reported Allah's Apostle (ﷺ) as having said this:
None amongst you should outbid another in a transaction, nor should he make proposals of marriage upon the proposal made by someone else.
Reference: Sahih Muslim 1412 a
In-book reference: Book 16, Hadith 57
USC-MSA web (English) reference(deprecated numbering scheme): Book 8, Hadith 3286