كتاب الشروط
Read the English translation first, with the original Arabic directly underneath.
Narrated Abu Huraira:
The Prophet (ﷺ) said, "No town-dweller should sell for a bedouin. Do not practice Najsh (i.e. Do not offer a high price for a thing which you do not want to buy, in order to deceive the people). No Muslim should offer more for a thing already bought by his Muslim brother, nor should he demand the hand of a girl already engaged to another Muslim. A Muslim woman shall not try to bring about The divorce of her sister (i.e. another Muslim woman) in order to take her place herself."
لاَ يَبِيعُ حَاضِرٌ لِبَادٍ، وَلاَ تَنَاجَشُوا، وَلاَ يَزِيدَنَّ عَلَى بَيْعِ أَخِيهِ، وَلاَ يَخْطُبَنَّ عَلَى خِطْبَتِهِ، وَلاَ تَسْأَلِ الْمَرْأَةُ طَلاَقَ أُخْتِهَا لِتَسْتَكْفِئَ إِنَاءَهَا