Sayyiduna Zayd bin Thabit (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "Part of the excellence of a person's Islam is that he leaves what does not concern him."
Al-Tabarani recorded it in al-Mu'jam al-Saghir; its chain contains Muhammad bin Kathir bin Marwan, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأدب / 12638