"Whoever is given a gift, then if he finds something let him reciprocate. If he has nothing, then let him mention some praise. For whoever has mentioned some praise, then he has expressed his gratitude. And whoever refrains (from doing so) then he has committed Kufr. And whoever pretends to be satisfied by that which he was not given, he is like the one who wears a garment of falsehood."  

عَنِ النَّبِيِّ ﷺ قَالَ مَنْ أُعْطِيَ عَطَاءً فَوَجَدَ فَلْيَجْزِ بِهِ وَمَنْ لَمْ يَجِدْ فَلْيُثْنِ فَإِنَّ مَنْ أَثْنَى فَقَدْ شَكَرَ وَمَنْ كَتَمَ فَقَدْ كَفَرَ وَمَنْ تَحَلَّى بِمَا لَمْ يُعْطَهُ كَانَ كَلاَبِسِ ثَوْبَىْ زُورٍ