Ma'qil bin Amir al-Asadi narrates: Abdullah bin Mas'ud (may Allah be pleased with him) passed by me while I was selling some goods of mine and swearing oaths over them. He began striking my head with something in his hand, saying: "Do not swear, for an oath may benefit the goods, but it wipes out the blessing."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8866