The Messenger of Allah ﷺ took my hand and said, "I love you, Muaz."I replied, "And I love you, Messenger of Allah."The Messenger of Allah ﷺ then said, "Never fail to say at the end of every prayer, 'My Lord, help me to remember You, to give thanks to You, and to worship You well.'"
أخبرنا يونس بن عبد الأعلى قال حدثنا ابن وهب قال سمعت حيوة يحدث عن عقبة بن مسلم عن أبي عبد الرحمن الحبلي عن الصنابحي
أخذ بيدي رسول الله ﷺ فقال إني لأحبك يا معاذ فقلت وأنا أحبك يا رسول الله فقال رسول الله ﷺ فلا تدع أن تقول في كل صلاة رب أعني على ذكرك وشكرك وحسن عبادتك
[Sahih] Abu Dawud reported it in the Book of Prayer, chapter on seeking forgiveness, hadith no. 1522, from the hadith of Haywa bin Shurayh, through him. It is also found in Sunan al-Kubra, hadith no. 1226. Ibn Khuzayma graded it sahih, hadith no. 751, as did Ibn Hibban, hadith no. 2345, and Hakim, according to the criteria of the two Shaykhs, 1/273, and Dhahabi agreed with him.