Quoted from Fatwas of shaykh bin Baz (rahimuhullah), part 26, p 366:
Praise be to Allah, the Lord of the Worlds, peace and blessings be upon the Messenger of Allah and upon his family and Companions. I read the story copied from the book entitled “Al-Tarikh” written by Ibn Jarir Al-Tabary (may Allah be merciful with him) regardingAmir Al-Mu’minin (Commander of the Believers)`Umar ibn Al-Khattab (may Allah be pleased with him) which reads as follows: “I followed him until he entered a house, and then he entered a room. I took permission to enter and I was given it. When I entered, I found him sitting on a mat and leaning on two pillows made of leather and stuffed with palm fibers. He gave me one of them to sit on. I saw a hall in which there was a curtain. He said, “O, Um Kulthum! Bring us lunch.” She brought him bread, oil and salt. He said, “O, Um Kulthum! Shall you come out and eat with us?” She said, “I hear the voice of a man with you.” He said, “Yes, and I do not think he is one of the residents of the country.” She said, “If you wanted me to sit with men, you would bring me clothes like those brought by Ibn Ja`far to his wife, by Al-Zubayr to his wife or by Talhah to his wife.” He said, Is it not enough for you to be said that Um Kulthum bint `Ali ibn Abu Talib and the wife of Amir Al-Mu’minin `Umar?” He said: “Come on, eat. If she had been satisfied, she would have made you better food than this.”
This tale is false; it is not true according to rules of transmission and the principles to verifying the meaning of the text. First: it is narrated by a group of weak narrators; some of them are accused of being liars and the direct source of this tale from `Umar is an unknown person. Thus, it is false according to the rules of transmission.
According to the principles of understanding the text, it is also false due to some reasons:
First, it contradicts what is known about `Umar (may Allah be pleased with him), his strictness in Hijab (veil), his extreme jealousy and his care that the Prophet should screen his wives until Allah (Exalted be He) revealed the Ayah (Qur’anic verse) concerning Hijab.
Second, it contradicts the rulings of Islam that were well-known to `Umar and any other scholar. The Qur’an and Sunnah (whatever is reported from the Prophet) prove the obligation of wearing Hijab and the prohibition of free intermixing (of men and women)in a way that causes Fitnah (temptation).
Third, its text is completely and logically rejected by anyone who contemplates it. In any case, this tale about `Umar is undoubtedly fabricated, whether to slander him, call for the free intermixing of men and women, or for other evil purposes. May Allah grant us safety!
Shaykh Abu Turab Al-Zhahiry, Shaykh Muhammad Ahmad Hisany and Dr. Hashim Bakr Habashy did well in their reply to this tale, clarifying its fabrication, and making it clear that such a tale cannot be attributed to Amir Al-Mu’minin `Umar ibn Al-Khattab (may Allah be pleased with him). May Allah reward them well, double their reward, grant us and them more knowledge and success and make us and them of the supporters of Al-Haqq (the Truth).
Out of taking part in the clarification of truth and refutation of falsehood, I found it necessary to write this brief statement to enlighten readers that this tale is false and degrading based on the reasons mentioned above. May Allah guide us all to the straight path and save us from the evils of ourselves and our misdeeds! He is All-Hearing, Ever-Near. May Allah’s Peace and Blessings be upon our Prophet Muhammad!