Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
nasai-kubra:6051 – Isḥāq b. Ibrāhīm > Abū Muʿāwiyah > ʿUbaydullāh > Nāfiʿ > Ibn ʿUmar

"Do not urge someone to cancel a sale he has already agreed upon so as to sell him your own goods, unless he bys or changes his mind." (Using translation from Nasāʾī 4504)  

الكبرى للنسائي:٦٠٥١ – أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ قَالَ حَدَّثَنَا أَبُو مُعَاوِيَةَ قَالَ حَدَّثَنَا عُبَيْدُ اللهِ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ

عَنْ رَسُولِ اللهِ ﷺ قَالَ «لَا يَبِيعُ الرَّجُلُ عَلَى بَيْعِ أَخِيهِ حَتَّى يَبْتَاعَ أَوْ يَذَرَ»  

See similar narrations below:

Collected by Nasāʾī, Ibn Mājah, Suyūṭī
nasai:4504 – Isḥāq b. Ibrāhīm > Abū Muʿāwiyah > ʿUbaydullāh > Nāfiʿ > Ibn ʿUmar

"Do not urge someone to cancel a sale he has already agreed upon so as to sell him your own goods, unless he bys or changes his mind."  

النسائي:٤٥٠٤ – أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ قَالَ حَدَّثَنَا أَبُو مُعَاوِيَةَ قَالَ حَدَّثَنَا عُبَيْدُ اللَّهِ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ

عَنْ رَسُولِ اللَّهِ ﷺ قَالَ لاَ يَبِيعُ الرَّجُلُ عَلَى بَيْعِ أَخِيهِ حَتَّى يَبْتَاعَ أَوْ يَذَرَ  

ibnmajah:2172 – Hishām b. ʿAmmār > Sufyān > al-Zuhrī > Saʿīd b. al-Musayyab > Abū Hurayrah

"A man is not to undersell his brother, nor is he to fry to outhaggle his brother."  

ابن ماجة:٢١٧٢ – حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ حَدَّثَنَا سُفْيَانُ عَنِ الزُّهْرِيِّ عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ عَنْ أَبِي هُرَيْرَةَ

عَنِ النَّبِيِّ ﷺ قَالَ لاَ يَبِيعُ الرَّجُلُ عَلَى بَيْعِ أَخِيهِ وَلاَ يَسُومُ عَلَى سَوْمِ أَخِيهِ