Sahih al-Bukhari Book 34, Hadith 93
A man decided that a slave of his would be manumitted after his death and later on he was in need of
money, so the Prophet (ﷺ) took the slave and said, "Who will buy this slave from me?" Nu'aim bin
`Abdullah bought him for such and such price and the Prophet (ﷺ) gave him the slave.
Allah's Messenger (ﷺ) forbade the selling of things by a town dweller on behalf of a desert dweller; and similarly Najsh was forbidden. And one should not urge somebody to return the goods to the seller so as to sell him his own goods; nor should one demand the hand of a girl who has already been engaged to someone else; and a woman should not try to cause some other woman to be divorced in order to take her place.
Allah's Messenger (ﷺ) forbade Najsh.