It wasnarrated from Abu Hurairah that the Messenger of Allah (ﷺ)said:
"If a person prays in public and does it well, and he prays insecret and does it well, then Allah says: 'This man is truly Myslave.'" (RU)
English reference (RU): Vol. 5, Book 37, Hadith 4200 (RU)
Arabic reference (RU): Book 37, Hadith 4340 (RU)