Sunan Ibn Majah
4200
Daif+3

It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) said:“If a person prays in public and does it well, and he prays in secret and does it well, then Allah says: ‘This man is truly My slave.’”

DaifAl-Albani
DaifMuhammad Fouad Abd al-Baqi