Hadith 517410
Chapter 53: Greetings - كتاب السلام
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 that Abdullah ibn Umar said that the Messenger of Allah, may Allah bless him and grant him peace, said, "When a jew greets you, and says 'Death to 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'."
Reference Muwatta Malik 517410
USC-MSA web (English) reference : Book 53, Hadith 3