Musnad Abu Ya'la al-Mawsili 2:4

Abu Khaythama Zuhayr ibn Harb narrated to us, Jarir ibn Abd al-Hamid narrated to us, from Abd al-Malik ibn Umayr, from Jabir ibn Samura, who said: Umar ibn al-Khattab addressed the people at al-Jabiya and said: "Indeed, the Messenger of Allah (may Allah bless him and grant him peace) stood in a position like this position of mine and said: 'Treat my companions well, then those who follow them, then those who follow them. Then falsehood will spread, until a man will swear an oath before he is asked to swear, and he will bear witness before he is asked to bear witness. So whoever among you desires to attain 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 the two. Beware, let no man be alone with a woman, for the third of them is the devil. Beware, and whoever among you is saddened by his evil deed and gladdened by his good deed, then he is a believer.'"