Imam Al-Nawawi’s Riyad-us-Saliheen
Chapter 318
Abomination of Swearing in Transaction

1720. Abu Hurairah (May Allah be pleased with him) said: I heard the Messenger of Allah (sallallaahu ’alayhi wa sallam) saying, “Swearing produces a ready sale for a commodity, but blots out the blessing.”
[Al-Bukhari and Muslim].

1721. Abu Qatadah (May Allah be pleased with him) said: I heard the Messenger of Allah (sallallaahu ’alayhi wa sallam) saying, “Beware of excessive swearing in sale, because it may promote trade but this practice will eliminate the blessing.”
[Muslim].