Jabir ibn 'Abdullah al-Ansari reported that the Prophet, may Allah bless him and grant him peace, said, "Whoever has a favour done for him should repay it. If he cannot find anything he can use to repay it, he should praise the one who did it. When he praises him, he thanks him. If he is silent, he is ungrateful to him. If someone adorns himself with something he has not been given, it is as if he was wearing a false garment."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا سَعِيدُ بْنُ عُفَيْرٍ قَالَ: حَدَّثَنِي يَحْيَى بْنُ أَيُّوبَ، عَنْ عُمَارَةَ بْنِ غَزِيَّةَ، عَنْ شُرَحْبِيلَ مَوْلَى الأَنْصَارِ، عَنْ جَابِرِ بْنِ عَبْدِ اللهِ الأَنْصَارِيِّ قَالَ: قَالَ النَّبِيُّ صلى الله عليه وسلم: مَنْ صُنِعَ إِلَيْهِ مَعْرُوفٌ فَلْيُجْزِئْهُ، فَإِنْ لَمْ يَجِدْ مَا يُجْزِئُهُ فَلْيُثْنِ عَلَيْهِ، فَإِنَّهُ إِذَا أَثْنَى فَقَدْ شَكَرَهُ، وَإِنْ كَتَمَهُ فَقَدْ كَفَرَهُ، وَمَنْ تَحَلَّى بِمَا لَمْ يُعْطَ، فَكَأَنَّمَا لَبِسَ ثَوْبَيْ زُورٍ.
sunnah.com