حَدَّثَنِي عَنْ مَالِكٍ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّهُ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ إِنَّ الْيَهُودَ إِذَا سَلَّمَ عَلَيْكُمْ أَحَدُهُمْ فَإِنَّمَا يَقُولُ السَّامُ عَلَيْكُمْ ‏.‏ فَقُلْ عَلَيْكَ ‏"‏ ‏.‏

Yahya related to me from Malik from Abdullah ibn Dinar thatAbdullah ibn Umar said that the Messenger of Allah, may Allah blesshim and grant him peace, said, "When a jew greets you, and says 'Deathto you' (as-samu alaykum) say, 'And to you.' " Yahya said,"Malik was asked whether a person who greeted a jew or christian,should apologise for it. He said, 'No'." Translation Not Available

Book Ref: Muwatta Imam Malik Book 53 Hadith 1761
Web Ref:  Muwatta Imam Malik Book 53 Hadith 3