The Prophet ﷺ took him by the hand one day and said, "Muaz, I truly love you."Muaz replied, "May my father and mother be ransomed for you, Messenger of Allah, I love you too."He said, "I advise you, Muaz, never neglect to say at the end of every prayer, 'O Allah, help me to remember You, to thank You, and to worship You well.'"Muaz passed this counsel on to Sanabihi, Sanabihi passed it on to Abu Abdul-Rahman, and Abu Abdul-Rahman passed it on to Uqba bin Muslim.
حدثنا عبد الله حدثني أبي حدثنا المقري حدثنا حيوة قال سمعت عقبة بن مسلم التجيبي يقول حدثني أبو عبد الرحمن الحبلي عن الصنابحي
أن النبي ﷺ أخذ بيده يوما ثم قال يا معاذ إني لأحبك فقال له معاذ بأبي أنت وأمي يا رسول الله وأنا أحبك قال أوصيك يا معاذ لا تدعن في دبر كل صلاة أن تقول اللهم أعني على ذكرك وشكرك وحسن عبادتك قال وأوصى بذلك معاذ الصنابحي وأوصى الصنابحي أبا عبد الرحمن وأوصى أبو عبد الرحمن عقبة بن مسلم
Its isnad is sahih, its narrators are trustworthy and have already been mentioned. Sanabihi is Abdul-Rahman bin Usayla, Abu Abdullah, a trustworthy narrator whose hadith is accepted by all the compilers, and he is one of the senior Tabiin. He entered Madinah five days after the death of the Prophet ﷺ.The hadith was narrated by Abu Dawud, 1/180, no. 1522, in the book of Prayer, chapter on seeking forgiveness, and Hakim graded it sahih, 1/273, and Dhahabi agreed with him.