“The idea of Christ is much older than Christianity.”

As quoted by William Rees-Mogg in The Times [London] (4 April 2005) {not found}. Gandhi here makes reference to a statement of Jesus: “No servant can serve two masters; for either he will hate the one and love the other, or else he will be loyal to the one and despise the other. You cannot serve God and mammon." (Luke 16:13); also partly quoted in Christianity in the Crosshairs: Real Life Solutions Discovered in the Line of Fire (2004, p. 74 books.google http://books.google.de/books?id=I7_5OM2VWuMC&pg=PA74) by Bill Wilson.
A variation is found in Bombay Sarvodaya Mandal & Gandhi Research Foundation's website mkgandhi.org http://www.mkgandhi.org/africaneedsgandhi/gandhi's_message_to_christians.htm. Christian missionary E. Stanley Jones, who spent much time with Gandhi in India, is said to have askedː “Mr Gandhi, though you quote the words of Christ often, why is it that you appear to so adamantly reject becoming his follower?". To this, Gandhi is said to have repliedː “Oh, I don’t reject your Christ. I love your Christ. It is just that so many of you Christians are so unlike your Christ”. Jones would write a book called " Mahatma Gandhi: An Interpretation https://archive.org/details/mahatmagandhiani000019mbp" (1948), where he included excerpts of his personal correspondance with Gandhi, but he did not include this conversation.
No further sources for Gandhi have been yet found; but a A similar quote is attributed to Bara Dadaː "Jesus is ideal and wonderful, but you Christians -- you are not like him." Source - Jones, E. Stanley. The Christ of the Indian Road, New York: The Abingdon Press,1925. (Page 114)
Disputed
Context: I like your Christ. I do not like your Christians. Your Christians are so unlike your Christ. The materialism of affluent Christian countries appears to contradict the claims of Jesus Christ that says it's not possible to worship both Mammon and God at the same time.

The Erasmus Reader (1990), pp. 140-141.
Handbook of the Christian Soldier (1503)

As quoted by William Rees-Mogg in The Times [London] (4 April 2005) {not found}. Gandhi here makes reference to a statement of Jesus: “No servant can serve two masters; for either he will hate the one and love the other, or else he will be loyal to the one and despise the other. You cannot serve God and mammon." (Luke 16:13); also partly quoted in Christianity in the Crosshairs: Real Life Solutions Discovered in the Line of Fire (2004, p. 74 books.google http://books.google.de/books?id=I7_5OM2VWuMC&pg=PA74) by Bill Wilson.
A variation is found in Bombay Sarvodaya Mandal & Gandhi Research Foundation's website mkgandhi.org http://www.mkgandhi.org/africaneedsgandhi/gandhi's_message_to_christians.htm. Christian missionary E. Stanley Jones, who spent much time with Gandhi in India, is said to have askedː “Mr Gandhi, though you quote the words of Christ often, why is it that you appear to so adamantly reject becoming his follower?". To this, Gandhi is said to have repliedː “Oh, I don’t reject your Christ. I love your Christ. It is just that so many of you Christians are so unlike your Christ”. Jones would write a book called " Mahatma Gandhi: An Interpretation https://archive.org/details/mahatmagandhiani000019mbp" (1948), where he included excerpts of his personal correspondance with Gandhi, but he did not include this conversation.
No further sources for Gandhi have been yet found; but a similar quote is attributed to Bara Dadaː "Jesus is ideal and wonderful, but you Christians -- you are not like him." Source - Jones, E. Stanley. The Christ of the Indian Road, New York: The Abingdon Press,1925. (Page 114)
Disputed

The Divine Commodity: Discovering A Faith Beyond Consumer Christianity (2009, Zondervan)

[Sam Harris, September 2007, http://www.samharris.org/site/full_text/the-problem-with-atheism, "The Problem with Atheism", On Faith, 2014-05-21]
2000s

Book IV, Chapter 4, "Good Infection"
Mere Christianity (1952)

Book 6: "Widow Kang", Ch. 3
The Years of Rice and Salt (2002)