Question to Al-Allaamah Ahmad An-Naajmi (rahimahullaah)
What is the ruling on the saying [Shukran (i.e. thank you)] to the one who did good to a person?
Whoever does so [i.e. says Shukran ] has indeed abandoned what is better and that is the statement [جزاك الله خير – May Allaah reward you with good]
[Source: Fath Ar-Rabb Al-Wadood Fil Fataawaa War-Rasaa’il War-Rudood’ 1/68]