A hadith and commentary.
The Prophet, peace and blessings of Allah be upon him, said:
"Whoever receives a favor and says to the one who did it,
'May Allah reward you with goodness' (Jazak Allahu khayran),
has indeed expressed the highest form of praise."
Narrated by al-Tirmidhi and al-Nasa'i.
Commentary:
Our religion urges us to thank those who do good and to reciprocate kindness.
Let us be diligent in expressing gratitude and praise in all its forms.
Among these is expressing thanks through words.
The most beautiful and eloquent of these is this noble phrase:
"May Allah reward you with goodness."