The Prophet ﷺ said, "Do not engage in najsh."
حدثنا أحمد بن عمرو بن السرح حدثنا سفيان عن الزهري عن سعيد بن المسيب
قال النبي ﷺ لا تناجشوا
No references are available.
Bukhari reported it in the Book of Sales, in the chapter "No one should sell against his brother's sale, etc.," hadith no. 2140, and Muslim reported it in the Book of Marriage, in the chapter on the prohibition of proposing marriage against a brother's proposal until he gives permission or withdraws, hadith no. 1413, both from the hadith of Sufyan bin Uyayna, through this same chain.