Two statements attributed to the Prophet Muhammad about the treatment of non-Muslims

“Whoever kills a person who has a truce with the Muslims will never smell the fragrance of Paradise.”

This hadith is reportedly to be found in the Sahih Muslim.

“Beware!  Whoever is cruel and hard on a non-Muslim minority, or curtails their rights, or burdens them with more than they can bear, or takes anything from them against their free will, I will complain against that person on the Day of Judgment.”

This hadith is, I’m told, attested in the Sunan Abi Dawud.

For both hadith, see here.  I haven’t yet checked the original source.