Musannaf Ibn Abi Shayba 33:828

Zayd ibn al-Hubab narrated to us, he said: Mu'awiyah ibn Salih informed us, he said: 'Amr ibn Qays al-Kindi informed me, from 'Abdullah ibn Busr, that a Bedouin said: "O Messenger of Allah, the laws of Islam have become many for me, so inform me of something I may hold fast to." He said: "Let your tongue remain moist with the remembrance of Allah."