The following is how Islam’s second caliph – Umar ibn al-Khattab (May Allah be pleased with him) treated Christians after the conquest of Jerusalem.
“In the name of God, the Merciful, the Compassionate. This is the assurance of safety which the servant of God, Umar, the Commander of the Faithful, has given to the people of Jerusalem. He has given them an assurance of safety for themselves for their property, their churches, their crosses, the sick and healthy of the city and for all the rituals which belong to their religion. Their churches will not be inhabited by Muslims and will not be destroyed. Neither they, nor the land on which they stand, nor their cross, nor their property will be damaged. They will not be forcibly converted. No Jew will live with them in Jerusalem.
The people of Jerusalem must pay the taxes like the people of other cities and must expel the Byzantines and the robbers. Those of the people of Jerusalem who want to leave with the Byzantines, take their property and abandon their churches and crosses will be safe until they reach their place of refuge. The villagers may remain in the city if they wish but must pay taxes like the citizens. Those who wish may go with the Byzantines and those who wish may return to their families. Nothing is to be taken from them before their harvest is reaped.
If they pay their taxes according to their obligations, then the conditions laid out in this letter are under the covenant of God, are the responsibility of His Prophet, of the caliphs and of the faithful.”
When Umar entered Jerusalem and the time of prayer arrived, the Christians offered him to pray in a church but he refused as he didn’t want the Muslims to use it as an excuse to convert it into a Mosque. He prayed nearby and this is the place where a mosque called ‘Masjid Umar ibn al-Khattab’ was built.
Islam guarantees the rights of minority religious groups under its control and ensures their safety. Christians and Jews prospered under Islamic states for hundreds of years and even gave refuge to those fleeing persecution.