Is it permissible for a Muslim to use certain phrases toward a disbeliever who has done him a favor, such as "thank you" or "may you be rewarded with good"?

The questioner : He says: Is it permissible for me to use certain phrases toward a disbeliever who has done me a favor, such as "thank you" or "may you be rewarded with good"?

The Shaykh : Yes, this falls under the saying of the Messenger (peace and blessings be upon him): So if someone other than a Muslim does you a favor, reward him, for this is part of the character of Islam. Perhaps this will reconcile his heart, so that he loves the Muslims and embraces Islam.