Many instances are on record when Umar gave a particular opinion and that opinion was later on corroborated by Allah and conurmation thereof was communicated to the Holy Prophet through Gabriel. That is why the Holy Prophet repeatedly said:
"God speaks through the tongue of Umar."
Umar suggested that the station of Abraham in Mecca should be used as a place of prayer. Later an injunction to this effect was revealed to the Holy Prophet.
Umar suggested that the wives of the Holy Prophet should be veiled. Later a verse was revealed enjoining the wives of the Holy Prophet to be veiled.
Umar suggested that the use of wine should be prohibited. Thereafter God enjoined the prohibition of wine.
'Abdullah b. Ubbay though a Muslim was insincere in his professions and was the enemy of God and the Holy Prophet. When he died the Holy Prophet led his funeral prayer. Umar suggested that the Holy Prophet should not pray at the funeral of those who were the enemies of God and the Prophet. A verse was later revealed enjoining the Holy Prophet not to pray at the funeral of those who were the enemies of God and His Prophet.
When there was an imputation against the conduct of 'Ayesha, Umar said that this was a grievous calumny. Later a verse was revealed declaring the episode as a calumny and establishing 'Ayesha's innocence.
After the battle of Badr, it was decided that the prisoners of the Quraish should be released on ransom. Umar said that the prisoners being the enemies of God should be killed. Later according to a revelation the Holy Prophet was enjoined that the enemies of God should be killed.
When the Azan was originally proposed the contents of the call were:
"I testify that there is no god but Allah-come ye to prayers."
Umar suggested, "The words 'I testify that Muhammad is the Messenger of God' should be added". A revelation corroborated this suggestion.
The practice was that people went to see the Holy Prophet unannounced. Umar suggested that all visitors should seek permission before being admitted to the presence of the Holy Prophet. A verse was later revealed enjoining the asking of permission before entering the presence of the Holy Prophet.
Once two persons to a dispute referred the case to the Holy Prophet and the Holy Prophet gave his verdict. One of them appealed against the decision of the Holy Prophet. Umar slew him with his sword. A verse was revealed absolving Umar from the death of the person who did not believe in the judgment of the Holy Prophet.
Once a Jew said to Umar, "Verily Gabriel who speaks to your Master is our enemy." Umar retorted, "Whosoever is an enemy to God, or His angels, or His Apostles, or Gabriel, or Michael, verily God is an enemy to the unbelievers." Later a verse was revealed declaring that God was the enemy of unbelievers.