Riyad as-Salihin, Book 18, Hadith 1780 (In-Book) ⓘ

'Uqbah bin 'Amir (May Allah be pleased with him) said: The Messenger of Allah 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].

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)‏‏)‏‏.‏