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