Yahya related to me from Malik from Zayd ibn Aslam from Ata ibnYasar that Muawiya ibn Abi Sufyan sold a gold or silver drinking-vessel for more than its weight. Abu'dDarda said, "I heard theMessenger of Allah, may Allah bless him and grant him peace,forbidding such sales except like for like." Muawiya said to him, "Idon't see any harm in it." Abu'd-Darda said to him, "Who will excuseme from Muawiya? I tell him something from the Messenger of Allah, mayAllah bless him and grant him peace, and he gives me his own opinion!I will not live in the same land as you!" Then Abu'd-Darda went toUmar ibn al-Khattab and mentioned that to him. Umar ibn al-Khattabtherefore wrote to Muawiya, "Do not sell it except like for like,weight for weight."
USC-MSA web (English) reference: Book 31, Hadith 33
Arabic reference: Book 31, Hadith 1324