(6) باب تَحْرِيمِ الْخِطْبَةِ عَلَى خِطْبَةِ أَخِيهِ حَتَّى يَأْذَنَ أَوْ يَتْرُكَ
Abu Huraira (Allah be pleased with him) reported Allah's Messenger (ﷺ) as having said this:
Do not outbid in a sale in order to ensnare. No man should enter into a transaction in which his brother has already entered, and no dweller of the town should sell on behalf of the villager. And no man should make a proposal of marriage which his brother has already made and no woman should ask for the divorce of another (co-wife) in order to deprive her of what belongs to her.
Reference: Sahih Muslim 1413 b
In-book reference: Book 16, Hadith 62
USC-MSA web (English) reference(deprecated numbering scheme): Book 8, Hadith 3290