When Caliph Umar had conquered Jerusalem, the local Bishop payed a visit and invited him to pray in his church. The Caliph declined, although his religion would have allowed him to do so.
When the Bishop inquired the reason for this rejection, the Caliph answered:
“I myself would love to pray in your church. Alas - I am afraid, my Muslim Brothers will claim your church simply because I prayed there once.”