The Messenger of Allah ﷺ took him by the hand and said, "Muaz, by Allah, I love you." Then he said, "I advise you, Muaz, never to fail at the end of every prayer to say, 'O Allah, help me to remember You, to thank You, and to worship You well.'"
أن رسول الله ﷺ أخذه بيده وقال: يا معاذ والله إني لأحبك فقال: أوصيك يا معاذ لا تدعن في دبر كل صلاة تقول: اللهم أعني على ذكرك وشكرك وحسن عبادتك.
Reported by Abu Dawud (1522), and this is his wording, and Nasai (1303), both through the route of Haywa bin Shurayh, who said, I heard Uqba bin Muslim say, Abu Abdul-Rahman Hubli told me, from Sanabihi, from Muaz bin Jabal, and he related it.Nasai added, after the Prophet's ﷺ words to Muaz, "By Allah, I love you," that Muaz said, "And I love you too, Messenger of Allah."Abu Dawud said, Muaz enjoined this upon Sanabihi, and Sanabihi enjoined it upon Abu Abdul-Rahman. Nasai added, in Al-Yaum wal-Laylah (109), that Abu Abdul-Rahman enjoined it upon Uqba bin Muslim.Nawawi said in Al-Khulasa, its isnad is sahih. Nasb Raya (2/235). Hakim said (3/273), sahih according to the standard of the two shaykhs.I say, Abu Abdul-Rahman Hubli, who is Abdullah bin Yazid Maafiri, is among the narrators of Muslim alone, though he is trustworthy.