Riyad as-Salihin 1780
'Uqbah bin 'Amir (May Allah be pleased with him) said:
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] .
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)‏‏)‏‏.‏