Sahih Muslim Book 26, Hadith Number 5387.

Chapter : Prohibition of saying first as-Salam-u-Alaikum to the people of the book, and how their salutations should be responded.

This hadith has been reported on the authority of A’znash with a slight variation of wording. ‘Aisha understood their meaning and cursed them and Allah’s Messenger (may peace be upon him) said: ‘Aisha. (do not do that) for Allah does not like the use of harsh words, and it was at this stage that this verse of Allah, the Exalted and Glorious has revealed: “And when they come to thee, they greet thee with a greeting with which Allah greets thee not” (iviii. 8) to the end of the verse.