Musannaf Ibn Abi Shayba 33:1491

Muhammad ibn Abd Allah narrated to us, he said: Ibn Abi Rawad narrated to us that a group of people accompanied Umar ibn Abd al-Aziz. He said: "Upon you is the fear of Allah, alone, with no partner for Him. And beware of joking, for it draws out the ugly and inherits rancor. Sit together with the Quran and speak [of it]. If it becomes heavy upon you, then [speak] of the speech of men. So proceed in the name of Allah."