Sayyiduna ‘Abdullah ibn Busr رضي الله عنه reports that a man once said:_

O Rasulullah, ‘The (optional) ‘ibadat have become too much for me, inform me of something that I should rather cling on to’.

Rasulullah صلى الله عليه وسلم replied:

‘Your tongue should remain moist with the remembrance of Allah’

(Sunan Tirmidhi, Hadith: 3375 and Sunan Ibn Majah, Hadith: 3794)