Musnad Ahmad 1101:17

Sufyan narrated to us, from Ibn Abi Najih, from Mujahid, that Sa'id ibn al-'As sent a delegation from Iraq to Uthman, and they came praising him. So al-Miqdad began throwing dust into their faces, and he said: "The Messenger of Allah, peace and blessings of Allah be upon him, commanded us to throw dust into the faces of the praisers." And Sufyan said once: So al-Miqdad stood up and said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "Throw dust into the faces of the praisers." Al-Zubayr said: "As for al-Miqdad, he has fulfilled what was upon him."