2:256 لاَ إِكْرَاهَ فِي الدِّينِ

When Umar ruled the still expanding Muslim state he had a talented slave called Asbaq who reports: “Umar was my master and I was a Christian. He used to speak to me about Islam and call on me to become a Muslim. He also said to me: ‘If you become a Muslim, I will get you to help me to discharge the trust God has given me in looking after the Muslim community. It is not permissible for me to put you in a position of trust with regard to the Muslim community when you belong to a religion other than theirs.’ But I refused. He used to say: ‘Well! I will not compel you, as no compulsion is admissible in religion.’ Shortly before his death, he set me free and told me: “You can go wherever you wish.”
his freedom of belief is supported by another report in which Umar, the caliph, was willing to speak to an old woman about Islam, inviting her to accept it.

Aslam, Umar’s servant, reports that when he accompanied Umar on his trip to Syria, he once brought him water for his ablution. Umar said to him: “Where did you get this water. I have never used a finer and sweeter water, not even rain water.”

Aslam said: “I got it from the home of an old Christian woman.”

When he finished his ablution, he went to her and said: “Old lady! You may wish to become a Muslim, because God has sent Muhammad with the religion of the truth.”

She uncovered her head to reveal that she had gone totally gray, and said: “I am but an old woman who is awaiting her death.”

Umar said no more than: “My Lord! Be my witness.”