Musnad Abu Ya'la al-Mawsili 2:2

Shayban narrated to us, Jarir ibn Hazim narrated to us, he said: I heard Abd al-Malik ibn Umayr narrating from Jabir ibn Samurah al-Suwa'i, and he said: Umar ibn al-Khattab delivered a sermon to us at al-Jabiyah and said: "O people, the Messenger of Allah (may Allah bless him and grant him peace) stood among us just as I am standing among you today. He said: 'Treat my companions well, then those who follow them, then those who follow them. Then falsehood will spread until a man will bear witness to a testimony without being asked for it, and he will swear an oath without being asked for it. So whoever desires the center of Paradise, let him hold fast to the community (al-jama'ah), for the devil is with the one, and he is further away from two. Let no man among you be alone with a woman, for the devil is the third of the two. Whoever is pleased by his good deed and saddened by his evil deed, then he is a believer.'"