Not to cancel a bargain already agreed upon Sahih al-Bukhari 2139
Arabic hadith text
حَدَّثَنَا إِسْمَاعِيلُ، قَالَ حَدَّثَنِي مَالِكٌ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ "لاَ يَبِيعُ بَعْضُكُمْ عَلَى بَيْعِ أَخِيهِ "
Translation
Narrated `Abdullah bin `Umar
Allah's Messenger (ﷺ) said, "Do not urge somebody to return what he has already bought (i.e. in optional sale) from another seller so as to sell him your own goods."