Musannaf Ibn Abi Shayba 17:1013

Ibn Idris narrated to us, from Harun ibn Antara, from Sulaym ibn Hanzala, who said: We came to Ubayy ibn Ka'b to speak with him. When he stood up, we stood up to walk with him. Umar caught up with him, and Umar raised his whip at him. He (Ubayy) said: "O Commander of the Faithful, do you know what you are doing?" He (Umar) said: "It is a trial for the one being followed, and a humiliation for the follower."