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."