Yahya related to me from Malik from Yunus ibn Yusuf from Said ibnal-Musayyab that Umar ibn al-Khattab passed by Hatab ibn Abi Baltaawho was underselling some of his raisins in the market. Umar ibn al-Khattab said to him, "Either increase the price or leave our market." (IT)
USC-MSA web (English) reference: Book 31, Hadith 57 (IT)
Arabic reference (IT): Book 31, Hadith 1349 (IT)