Musnad Ahmad 17:8

Musa ibn Dawud narrated to us, Abdullah ibn Umar narrated to us, from Ibn Shihab, from Ali ibn al-Husayn, from his father, may Allah be pleased with him, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "From the excellence of a person's Islam is his leaving that which does not concern him."