Sahih al Bukhari 2139
Sales and Trade
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 ".
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
Text from the public-domain hadith-api dataset. Numbering follows that dataset and can differ by a few from some printed editions — check the wording, not only the number.