Musnad Ahmad 534:9

'Ali ibn 'Ayyash narrated to us, Hassan ibn Nuh narrated to us, from 'Amr ibn Qays, from 'Abdullah ibn Busr, who said: Two Bedouins came to the Prophet, may Allah bless him and grant him peace. One of them said: "Who is the best of men, O Muhammad?" The Prophet, may Allah bless him and grant him peace, said: "He whose life is long and whose deeds are good." The other said: "The laws of Islam have become many for us, so is there a door we can hold fast to that is comprehensive?" He said: "Let your tongue remain moist with the remembrance of Allah."