Omar ibn Al-Khattab harbored great respect for Ali ibn Abi-Talib, as the latter was of the family of Prophet Muhammad. This is evident in a narration by Ibn Abbas, reported by Az-Zamakhshari:
A man came to Omar complaining about Ali. Omar turned to Ali and said to him, "O Abi Al-Hassan, sit down with your opponent." Ali sat next to the litigant and started to debate with him until they finished. Then Ali returned to his seat, upon which Omar noticed that Ali seemed changed. Omar asked, " O Abi Al-Hassan, why do you seem changed?" Ali replied, "You called me with my epithet in the presence of an adversary. I wish you would have just said, 'Ali, stand up and go sit next to your opponent!' " Omar held Ali's head and kissed his forehead, then said, "May my father and mother be sacrificed for you! You are a means of guidance from Allah! How many a time has Allah employed you to bring us from darkness into light!" "You are such a haven in every distress and a solver of every juristic issue."
Omar also once said to him, "May I never outlive you, Ali"
Omar also showed his esteem of Ali ibn Abi Talib's juristic skill, saying, "May I not live to witness a juristic issue that Abi Al-Hassan is not there to solve."
On another occasion he said, "May I never be in a land where Abi Al-Hassan is not."
On a third occasion, Omar commented on Ali's judicial talents after the latter had solved a case in a very skillful manner:
" Women lack the ability to give birth to the like of Ali ibn Abi Talib. Were it not for Ali, Omar would have perished."
Scholar Ibn Asaker narrated in the History of Damascus that Omar pointed at Ali and said, "The most knowledgeable of our Prophet and his Book."
We continue Omar's comments on Ali's judicial and personal excellence. Ibn Asaker mentioned that Omar said, "Whatever opinion Ali says is the valid one."
Ibn Asaker also narrated an incident involving one of the Companions that shows how Caliph Omar ibn Al-Khattab highly appreciated Ali's legal opinions.  The narration goes, "I went to Omar ibn Al-Khattab in Mecca and said, 'I rode the horse until I reached you, where should I assume the state of Ihram (ritual consecration) to perform Umrah?' Omar replied, 'Ask Ali ibn Abi Talib.' The Companion returned to Omar and told him about Ali's opinion. Omar said, 'I cannot find any better opinion than that of Ali.' "
Scholar Al-Haskani narrated that Omar ibn Al-Khattab said: "Ali the most knowledgeable person of what Allah has sent down upon Prophet Muhammad, peace and blessings be upon him."
Scholar Ash-Shanqiti mentioned in his book, "Al-Kenayah", page 57, that Omar said to Ali, "You are the most reliable in issuing fatwas."
Imam Ahmad ibn Hanbal mentioned in his book, "Fadael As-Sahabah", that Omar said about Ali, "O Allah, don't afflict me unless Abi Al-Hassan is on my side."
Those words profoundly express Omar's deep love and appreciation for Ali, may Allah be pleased with them both.
A prominent aspect of the Caliphate of Omar ibn Al-Khattab was his relationship with Ali which was based on respect, admiration, love and cooperation in managing state affairs. This relationship has been deformed by some people who want to create dissent among Muslims. Such people are like some Safavid Shiites and their followers who falsified history and told false stories to suggest that the time of the Rightly-Guided Caliphs was a time of dissension and fighting over power, whereas those Caliphs were most indifferent to lowly worldly desires and the appetite for power.
Omar's admiration of Ali manifested itself someone accused Ali of being proud and arrogant. Omar replied, out of his love for Ali ibn Abi Talib, saying, "He should be proud, for his sword helped establish the pillars of Islam and he is the most knowledgeable judge and among the most honored of the nation."
Omar also said about him once, "Harms Ali is equal to harming the Prophet himself."
Omar never rejected nor turned down an opinion or request from Ali. He rather hurried to put them to effect out of conviction, admiration and trust for Ali's wisdom and extensive knowledge in religious matters.
Ali ibn Abi Talib's love for Omar ibn Al-Khattab is evident when the first dissuaded the latter from heading to Nahawand on top of the Muslim army to fight the Persians out of fear for the life of Omar. Omar followed Ali's advice in that too.