General Behavior (Kitab Al-Adab)
Dawud :: Book 41 : Hadith 4795
Narrated Jabir ibn Abdullah:
The Prophet (peace_be_upon_him) said: If someone is given something, he should give a return for it provided he can afford; if he cannot afford, he should praise him. He who praises him for it, thanks him, and he who conceals it is ungrateful to him.