Sunan an-Nasa'i 4503
It was narrated from Ibn 'Umar that the Prophet said:
"No one of you should urge someone to cancel a sale he has already agreed upon with his brother so as to sell him his own goods."
أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، عَنْ مَالِكٍ، وَاللَّيْثِ، - وَاللَّفْظُ لَهُ - عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، عَنِ النَّبِيِّ صلى الله عليه وسلم أَنَّهُ قَالَ ‏
"‏ لاَ يَبِيعُ أَحَدُكُمْ عَلَى بَيْعِ أَخِيهِ ‏"‏ ‏.‏