Musnad Ahmad 935:8

Abdullah narrated to us, Shaiban narrated to us, Hammad ibn Salamah narrated to us, al-Hajjaj ibn Artah narrated to us, from Abu Ishaq al-Hamdani, from Abdullah ibn Abi Basir, from Ubayy ibn Ka'b, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "If the people knew what virtue is in the Isha prayer and the dawn prayer in congregation, they would have come to them even if they had to crawl."