It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Noble Prophet (peace and blessings be upon him) said: "When a Jew greets you with Salam, he says «السام عليك», so in reply you should only say 'Alaik'."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 4698
Hadith Gradingحکم دارالسلام:إسناده صحيح، خ : 6928، م : 2164