Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) took hold of my hand and said: "O Mu'adh! I love you." I said: And by Allah, I love you too, O Messenger of Allah! He (peace and blessings be upon him) said: "I advise you with words that you should say after every prayer: 'Rabbi a'inni 'ala dhikrika wa shukrika wa husni 'ibadatik' (O my Lord, help me to remember You, to thank You, and to worship You well)."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17354