The Messenger of Allah ﷺ said, and Muhammad reported from the Prophet ﷺ, "Do not engage in najsh, and let no city dweller sell on behalf of a desert dweller. No man should sell against the sale of his brother, nor propose against the proposal of his brother, and no woman should ask for the divorce of her sister in order to empty what is in her vessel."
أخبرنا محمد بن منصور وسعيد بن عبد الرحمن قالا حدثنا سفيان عن الزهري عن سعيد
قال رسول الله ﷺ وقال محمد عن النبي ﷺ لا تناجشوا ولا يبع حاضر لباد ولا يبع الرجل على بيع أخيه ولا يخطب على خطبة أخيه ولا تسأل المرأة طلاق أختها لتكتفئ ما في إنائها
Bukhari, Sales, Chapter: "One should not outbid his brother, nor propose marriage while another has proposed," etc., no. 2140, and Muslim, Marriage, Chapter: The prohibition of proposing marriage to a woman already proposed to by one's brother, until he permits it or leaves it, no. 1413, from the hadith of Sufyan bin Uyayna, through him.