The Messenger of Allah ﷺ said, "None of you should sell over the sale of another." He forbade najsh, and he forbade the sale of habal al-habalah. He also forbade muzabanah, which is the sale of fresh dates for dried dates by measure, and the sale of grapes for Zabib by measure.
حدثنا محمد بن إدريس الشافعي رحمه الله أخبرنا مالك عن نافع
أن رسول الله ﷺ قال لا يبع بعضكم على بيع بعض ونهى عن النجش ونهى عن بيع حبل الحبلة ونهى عن المزابنة والمزابنة بيع الثمر بالتمر كيلا وبيع الكرم بالزبيب كيلا
Its chain of transmission is sahih. In reality this is four separate hadiths, which Imam Ahmad combined in this one chain of transmission. They have passed many times before, and I did not find them combined either in Muwatta or in the books of Shafii. If I could go back and redo what I have already done, I would have made them into four separate numbers in the Musnad.The first is the prohibition against people outbidding one another in a sale, which has passed many times, both alone and combined with others, including numbers 4531 and 4530. It appears in Muwatta 2:170, and in Ikhtilaf al-Hadith of Shafii (margin of al-Umm 7:187).The second is the prohibition against najsh, which has also passed many times together with the first, as in 4531 and 4530. It appears in Muwatta 2:171, and Ikhtilaf al-Hadith, page 185. The explanation of najsh from Ibn Athir has already been given, and here we add the explanation of Malik. He said, "Najsh means offering someone more than the value of his goods, without intending to buy them yourself, so that others follow your lead." And the explanation of Shafii, who said, "It means that a man is present when goods are being sold, and he offers a price for them while not wanting to buy, so that the bidders follow his lead and offer more than they would have offered had they not heard his bid." He said, "Whoever practices najsh is disobedient in doing so, if he knew that the Messenger of Allah ﷺ had forbidden it."The third is habl al-habalah, which has also passed many times, including number 394 following the musnad of Umar bin Khattab, and 4491 and 5307. It appears in Muwatta 2:149-150. I did not find it in the books of Shafii, or perhaps its location in them escaped me.The fourth is muzabanah, which has also passed many times, including numbers 4490 and 5330. It appears in Muwatta 2:128, in al-Umm of Shafii 3:54, in Ikhtilaf al-Hadith, page 319, and in al-Risalah with our commentary, number 906.