Musnad Ahmad 2:33

'Ali ibn Ishaq narrated to us, 'Abdullah—meaning Ibn al-Mubarak—informed us, Muhammad ibn Suqah informed us, from 'Abdullah ibn Dinar, from Ibn 'Umar: That 'Umar ibn al-Khattab delivered a sermon at al-Jabiyah and said: The Messenger of Allah (ﷺ) stood among us just as I am standing among you, and he said: "Treat my companions well, then those who follow them, then those who follow them. Then falsehood will spread, until a man will volunteer testimony before he is asked for it. So whoever among you 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. And whoever is gladdened by his good deed and saddened by his evil deed, then he is a believer."