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."' (ES)
English reference (ES): Vol. 3, Book 12, Hadith 2209 (ES)
Arabic reference (ES): Book 12, Hadith 2293 (ES)