Sunan an Nasai
1303
Sahih+2

It was narrated that Mu'adhbin Jabal said:"The Messenger of Allah (ﷺ) took my hand and said: 'I love you, O Mu'adh!' I said: 'And I love you, O Messenger of Allah (ﷺ).' Then the Messenger of Allah (ﷺ) said: 'Never forget to say in every prayer: Rabbi a'inni 'ala dhikrika wa shukrika wa husni 'ibadatik (My Lord, help me to remember You, give thanks to You and worship You well)

SahihAbu Ghuddah
SahihAl-Albani