Sahih al-Bukhari, Book 34, Hadith 91 (In-Book) ⓘ
Narrated `Abdullah bin `Umar: Allah's Messenger 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."
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 " .
also referenced under: Hadith 2139 (DarusSalam) & Volume 3, Book 34, Hadith 349 (USC-MSA)