Musnad Ahmad 17:3

Ibn Numayr and Ya‘la narrated to us, they said: Hajjaj—meaning Ibn Dinar al-Wasiti—narrated to us, from Shu‘ayb ibn Khalid, from Husayn ibn ‘Ali, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, part of the excellence of a person's Islam is speaking little about that which does not concern him."