On the authority of Abu Hurairah (radhiAllahu 'anhu), that he said: The Messenger of Allah (allayhis salat wassallam) said, "From the perfection of a person's Islaam is abstaining from what does not concern him". (Hadeeth Hasan related by Imaam at-Tirmidhee and other in this form)1
1)Related by at-Tirmidhee #2317, Ibn Majah #3976, Imaam Maalik in al-Muwatta; Sharhus-Sunnah #4133; Imaam Ahmad in al-Musnad #1737. Imam Nawwawi, al-Albaanee, Ibn abdel bar, Ibn hajar, Ibn qudamah graded it sahih. Some scholars of hadeeth say it is mursal (Mursal comes under weak hadeeth).