Sayyidah Aishah Siddiqah (may Allah be pleased with her) transmits this saying of the Prophet (peace and blessings be upon him): "Whoever has a kindness done to him should repay it; and if he is not able to, he should mention it, for whoever mentions it has thanked him for it. And whoever makes a show of being satisfied with something he was not given is like one who wears two garments of falsehood."
Ahmad, and al-Tabarani in al-Mu'jam al-Awsat, recorded it. Its chain contains a narrator, Salih bin Abi al-Akhdar, who has been declared trustworthy despite his weakness; the remaining narrators of Ahmad are thiqat (trustworthy).