Ali ibn Hussein reported: The Messenger of Allah, peace and blessings be upon him, said, “Verily, from the perfection of Islam is that a person leaves what does not concern him.”

Source: Sunan At-Tirmidhi 2318

Grade: Hasan (fair) according to An-Nawawi

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http://dailyhadith.abuaminaelias.com/2012/05/21/hadith-on-islam-perfection-in-islam-is-to-leave-what-is-unbeneficial/