'Abdu'r-Rahman said, "Ibn 'Umar passed by a Christian who greeted him and Ibn 'Umar returned the greeting He was told that the man was a Christian. When he learned that, he went back to him and said, 'Give me back my greeting.'"  

أَنَّهُ نَصْرَانِيٌّ فَلَمَّا عَلِمَ رَجَعَ إِلَيْهِ فَقَالَ رُدَّ عَلَيَّ سَلامِي