((جَزَاكَ اللَّهُ خَيْراً)).

jazaaka allahu khayraan.

(If someone does you a favour and you say: (May Allah reward you with goodness.) then you have indeed excelled in praising him.)

(If someone does you a favour and you say: (Jazakal-lahu khayran.) then you have indeed excelled in praising him.)