Sahih al-Bukhari 2087
Sahih al-Bukhari · Book 34: Sales and Trade · "Allah will destroy Riba and will give increase for Sadaqat"
Narrated Abu Huraira:
حَدَّثَنَا يَحْيَى بْنُ بُكَيْرٍ ، حَدَّثَنَا اللَّيْثُ ، عَنْ يُونُسَ ، عَنِ ابْنِ شِهَابٍ ، قَالَ ابْنُ الْمُسَيَّبِ إِنَّ أَبَا هُرَيْرَةَ ـ رضى الله عنه ـ قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " الْحَلِفُ مُنَفِّقَةٌ لِلسِّلْعَةِ مُمْحِقَةٌ لِلْبَرَكَةِ " .
I heard Allah's Messenger (ﷺ) saying, "The swearing (by the seller) may persuade the buyer to purchase the goods but that will be deprived of Allah's blessing."