Riyad as-Salihin, Book 18, Hadith 1779 (In-Book) ⓘ
Ibn 'Umar (May Allah be pleased with them) said: The Messenger of Allah said, "A person should not enter into a transaction when his (Muslim) brother has already negotiated, nor should he make a proposal of marriage when that of his brother is pending, except with the permission of the latter."[Al-Bukhari and Muslim]
وعن ابن عمر رضي الله عنهما، أن رسول الله صلى الله عليه وسلم قال: "لا يبع بعضكم على بيع بعض، ولا يخطب على خطبة أخيه إلا أن يأذن له" ((متفق عليه، وهذا لفظ مسلم))