Compiled by Imam Yahya ibn Sharaf al-Nawawi
وعن عقبة بن عامر أن رسول الله صلى الله عليه وسلم قال: "المؤمن أخو المؤمن، فلا يحل لمؤمن أن يبتاع على بيع أخيه ولا يخطب على خطبة أخيه حتى يذر" ((رواه مسلم)).
The Messenger of Allah (ﷺ) said, "A Mu'min is the brother of another Mu'min; and thus it is not permissible for a Mu'min to make an offer while the offer of his brother is pending, nor should he make a proposal of marriage while that of his brother is pending till he withdraws his proposal."[Muslim].