On the authority of Abu Hurayrah (may Allah be pleased with him) who said:

The Messenger of Allah (peace and blessings of Allah be upon him) said, “Part of the perfection of one’s Islam is his leaving that which does not concern him.” A hasan (good) hadeeth which was related by at-Tirmidhi and others in this fashion.

عَنْ أَبِي هُرَيْرَةَ رَضِيَ اللهُ عَنْهُ قَالَ: قَالَ رَسُولُ اللَّهِ صلى الله عليه و سلم "مِنْ حُسْنِ إسْلَامِ الْمَرْءِ تَرْكُهُ مَا لَا يَعْنِيهِ".
حَدِيثٌ حَسَنٌ، رَوَاهُ التِّرْمِذِيُّ [رقم: 2318] ، ابن ماجه [رقم:3976].
Reference : 40 Hadith Nawawi 12
English translation : Hadith 12