مِنْ حُسْنِ إسْلَامِ الْمَرْءِ تَرْكُهُ مَا لَا يَعْنِيهِ
From the completeness of a person’s Islaam
is that he leaves alone that which does not concern him.
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(Taken from Hadeeth 12 of Nawawi’s 40. At-Tirmidhee)