Malik bin Yukhamir al-Saksaki (may Allah have mercy on him) said that Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) told them: The last conversation between me and the Messenger of Allah (peace and blessings be upon him), upon which I parted from him, was that I asked: Which deed is most beloved to Allah? He (peace and blessings be upon him) said: "That you die while your tongue is moist with the remembrance of Allah."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17344