Sayyiduna Buraydah (may Allah be pleased with him) said: When the Messenger of Allah (peace and blessings be upon him) went out to the market, he would say: "Allahumma inni as'aluka min khayri hadhihi al-suq wa khayri ma fiha, wa a'udhu bika min sharriha wa sharri ma fiha. Allahumma inni a'udhu bika an usiba fiha yaminan fajiratan aw safqatan khasirah (O Allah, I ask You for the good of this market and the good of what is in it, and I seek refuge in You from its evil and the evil of what is in it. O Allah, I seek refuge in You from swearing a false oath in it or making a losing deal)."
Hadith Referenceالمعجم الكبير للطبراني / باب الباء / 1146