Mishkat al-Masabih 9 Supplications كتاب الدعوات 54

وَعَن عبد الله بن يسر: أَنَّ رَجُلًا قَالَ: يَا رَسُولَ اللَّهِ إِنَّ شَرَائِعَ الْإِسْلَامِ قَدْ كَثُرَتْ عَلَيَّ فَأَخْبِرْنِي بِشَيْءٍ أَتَشَبَّثُ بِهِ قَالَ: ” لَا يَزَالُ لِسَانُكَ رَطْبًا بِذكر اللَّهِ) رَوَاهُ التِّرْمِذِيُّ وَابْنُ مَاجَهْ وَقَالَ التِّرْمِذِيُّ: هَذَا حَدِيث حسن غَرِيب

‘Abdallah b. Busr told of a man saying, “Messenger of God, the ordinances of Islam are too many for me, so tell me something to which I may cling.” He replied, “Your tongue will continue to be supple by making mention of God.” Tirmidhi and Ibn Majah transmitted it. Tirmidhi saying this is a hasan gharib tradition.