It was narrated from Abu Qatadah that the Messenger of Allah (ﷺ), said:
"Beware of swearing oaths when selling, for it may help you to make a sale but it destroys the blessing."' (FR)
English reference (FR): Vol. 3, Book 12, Hadith 2209 (FR)
Arabic reference (FR): Book 12, Hadith 2293 (FR)