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. (DE)
Reference (DE): 40 Hadith Nawawi 12 (DE)
English translation (DE): Hadith 12 (DE)