Bulugh al-Maram, Book 13, Hadith 10 (In-Book) ⓘ

Narrated Usama bin Zaid (RA): Allah's Messenger said. "If one is done a kindness and [expresses his gratitude] to his benefactor by saying 'May Allah give you a good reward', he has fully expressed his appreciation." [at-Tirmidhi reported it, and Ibn Hibban graded it Sahih (authentic)].

وَعَنْ أُسَامَةَ بْنِ زَيْدٍ رَضِيَ اَللَّهُ عَنْهُمَا قَالَ: قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ "مَنْ صُنِعَ إِلَيْهِ مَعْرُوفٌ, فَقَالَ لِفَاعِلِهِ: جَزَاكِ اَللَّهُ خَيْراً.‏ فَقَدْ أَبْلَغَ فِي اَلثَّنَاءِ" } أَخْرَجَهُ اَلتِّرْمِذِيُّ, وَصَحَّحَهُ اِبْنُ حِبَّانَ 1‏.‏ ‏1 ‏- صحيح.‏ رواه الترمذي ( 2035 )‏، وابن حبان ( 3404 )‏ وقال الترمذي: " هذا حديث حسن جيد غريب".‏