On the contrary, he proclaimed his conversion publicly and challenged the Quraysh openly. He did not approve the Muslims' concealment of themselves, their secret movement from one end of Makkah to the other, and their holding of prayers at a safe distance from any Quraysh attack. Umar began to fight the Quraysh as soon as he entered the faith of Islam, constantly pressed his way close to the Kaaba, and performed his prayer there in company with whatever Muslims decided to join him. But these curious claims find little support in evidence. And if the evidence means anything, it appears to run counter to the claims themselves.
Some claims are even more extravagant.
For example, the Egyptian historian, Amin Dawidar, says in his book , Pictures From the Life of the Messenger of God , that Umar's conversion to Islam was a death blow to the Quraysh. What actually happened was that Umar's conversion to Islam synchronized with a new and an unprecedented wave of terror that broke over the Muslims. Whereas before his conversion only those Muslims were victims of persecution who had no one to protect them, now no Muslim, not even Muhammad Mustafa himself, was safe from the malevolence of the polytheists. According to one report a number of them had returned to Makkah, according to another, all. On reaching Makkah they realized that the Quraysh had resumed persecution of the Muslims with stronger hatred and renewed vigor .