I heard the Messenger of Allah ﷺ say, "The best remembrance is 'There is no god but Allah,' and the best supplication is 'All praise belongs to Allah.'"
سمعت رسول الله ﷺ يقول: أفضل الذكر لا إله إلا الله، وأفضل الدعاء الحمد الله.
Tirmidhi (3383) and Ibn Majah (3800) narrated it, and Ibn Hibban (846) and Hakim (1/498, and 503) both graded it sahih, all of them through the route of Musa bin Ibrahim bin Kathir Ansari, who said, "I heard Talha bin Kharash say, 'I heard Jabir bin Abdullah,'" and he mentioned it.Its chain is hasan because of Musa bin Ibrahim and Talha bin Kharash, for the two of them make the hadith hasan. Tirmidhi said, "This is a hasan gharib hadith, we do not know it except through the report of Musa bin Ibrahim, and Ali bin Madini and more than one other have narrated this hadith from this Musa bin Ibrahim." Hakim said, "This is a hadith sahih in chain."