It is narrated from Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) that he delivered a sermon at a place called Jabiyah and said: The Messenger of Allah (peace and blessings be upon him) stood among us as I stand among you and said: "Treat my Companions well, then those who come after them, then those who come after them. Then lying will become widespread, until a man gives testimony before he is asked for it and swears an oath before he is asked for it. Whoever among you wants the finest, central place in Paradise, let him hold fast to the Jama'ah, for Satan is with the one who is alone and he flees from two. No man should be alone with a woman, for Satan is the third with them. And whoever is pleased by his good deeds and grieved by his bad deeds is a believer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13521