Hadith 13:10
Narrated Usama bin Zaid (RA):
Allah's Messenger (ﷺ) 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
Original Reference: Bulugh al-Maram 1383