When the Jews offer you salutations, some of them say as-Sam-u-'Alaikum (death be upon you). You should say (in response to it): Let it be upon you. (Using translation from Muslim 2164a)  

قَالَ رَسُولُ اللهِ ﷺ إِنَّ الْيَهُودَ إِذَا سَلَّمُوا عَلَيْكُمْ يَقُولُ أَحَدُهُمُ السَّامُ عَلَيْكَ فَقُلْ عَلَيْكَ  

That the Messenger of Allah ﷺ said: "Indeed when a Jew gives Salam to one of you, then he is only saying: 'As-Samu 'Alaikum' (Death be upon you) so say: "Alaik (And upon you).'" (Using translation from Tirmidhī 1603)   

النَّبِيَّ ﷺ قَالَ إِذَا سَلَّمَ عَلَيْكَ الْيَهُودِيُّ وَالنَّصْرَانِيُّ فَإِنَّمَا يَقُولُ السَّامُ عَلَيْكُمْ فَقُلْ عَلَيْكُمْ  

Messenger of Allah ﷺ said, "When the Jews greet anyone of you they say: 'Sam'Alaika (death be upon you); so you should say; 'Wa 'Alaika (and upon you).'" (Using translation from Bukhārī 6928)   

عَنِ النَّبِيِّ ﷺ قَالَ إِنَّ الْيَهُودَ إِذَا سَلَّمُوا قَالُوا السَّامُ عَلَيْكُمْ فَقُولُوا وَعَلَيْكُمْ  

(the wife of the Prophet) A group of Jews entered upon the Prophet ﷺ and said, "As-Samu-Alaikum." (i.e. death be upon you). I understood it and said, "Wa-Alaikum As-Samu wal-la'n. (death and the curse of Allah be Upon you)." Messenger of Allah ﷺ said "Be calm, O ʿAisha! Allah loves that on, should be kind and lenient in all matters." I said, "O Messenger of Allah ﷺ! Haven't you heard what they (the Jews) have said?" Messenger of Allah ﷺ said "I have (already) said (to them) "And upon you ! " (Using translation from Bukhārī 6024)   

أَنَّ رَهْطًا مِنَ الْيَهُودِ دَخَلُوا عَلَى النَّبِيِّ ﷺ فَقَالُوا السَّامُ عَلَيْكَ قَالَ النَّبِيُّ ﷺ «عَلَيْكُمْ» فَقُلْتُ بَلْ عَلَيْكُمُ السَّامُ وَاللَّعْنَةُ قَالَ النَّبِيُّ ﷺ «يَا عَائِشَةُ إِنَّ اللهَ يُحِبُّ الرِّفْقَ فِي الْأَمْرِ كُلِّهِ» فَقُلْتُ يَا رَسُولَ اللهِ أَلَمْ تَسْمَعْ مَا قَالُوا؟ قَالَ قَدْ قُلْتُ عَلَيْكُمْ  

A group of Jews came to Messenger of Allah ﷺ and said, "As-samu 'Alaika " (Death be on you), and I understood it and said to them, "Alaikum AsSamu wa-l-la'na (Death and curse be on you)." Allah's Apostle said, "Be calm! O ʿAisha, for Allah loves that one should be kind and lenient in all matters." I said. "O Messenger of Allah ﷺ! Haven't you heard what they have said?" Messenger of Allah ﷺ said, "I have (already) said (to them), 'Alaikum (upon you).' " (Using translation from Bukhārī 6256)  

دَخَلَ رَهْطٌ مِنَ الْيَهُودِ عَلَى رَسُولِ اللهِ ﷺ فَقَالُوا السَّامُ عَلَيْكَ فَفَهِمْتُهَا فَقُلْتُ السَّامُ عَلَيْكُمْ وَاللَّعْنَةُ فَقَالَ رَسُولُ اللهِ ﷺ مَهْلًا يَا عَائِشَةُ إِنَّ اللهَ يُحِبُّ الرِّفْقَ فِي الْأَمْرِ كُلِّهِ قُلْتُ يَا رَسُولَ اللهِ أَلَمْ تَسْمَعْ مَا قَالُوا؟ قَالَ رَسُولُ اللهِ ﷺ قَدْ قُلْتُ عَلَيْكُمْ  

[Machine] A man from the Jews entered upon the Messenger of Allah ﷺ and said, "As-Samu Alaykum" (meaning, death be upon you). The Messenger of Allah ﷺ replied, "Wa Alaykum" (meaning, and upon you). I understood the meaning, so I said, "As-Samu Alaykum" and added, "and curse." The Messenger of Allah ﷺ said, "O Aisha, be gentle, for Allah loves kindness in all matters." I said, "O Messenger of Allah, did you not hear what he said to you?" He replied, "I did, and I responded by saying 'and upon you' 10144 times." 'Imran ibn Bakkar narrated to me, he said: Abu Al-Yaman informed us, he said: Shu'ayb narrated to us from Az-Zuhri, who narrated to me from Urwah, who said: A man from the Jews entered upon the Messenger of Allah ﷺ and mentioned something similar.  

دَخَلَ رَجُلٌ مِنَ الْيَهُودِ عَلَى رَسُولِ اللهِ ﷺ فَقَالَ السَّامُ عَلَيْكُمْ فَقَالَ «وَعَلَيْكُمْ» فَفَهِمْتُهَا فَقُلْتُ السَّامُ عَلَيْكُمْ وَاللَّعْنَةُ فَقَالَ رَسُولُ اللهِ ﷺ «يَا عَائِشَةُ عَلَيْكِ بِالرِّفْقِ فَإِنَّ اللهَ يُحِبُّ الرِّفْقَ فِي الْأَمْرِ كُلِّهِ» قُلْتُ يَا رَسُولَ اللهِ أَلَمْ تَرَ إِلَى مَا قَالَ السَّامُ عَلَيْكُمْ؟ قَالَ قَدْ قُلْتُ وَعَلَيْكُمْ 10144 أَخْبَرَنِي عِمْرَانُ بْنُ بَكَّارٍ قَالَ حَدَّثَنَا أَبُو الْيَمَانِ قَالَ أَخْبَرَنَا شُعَيْبٌ عَنِ الزُّهْرِيِّ أَخْبَرَنِي عُرْوَةُ أَنَّ عَائِشَةَ قَالَتْ دَخَلَ رَجُلٌ مِنَ الْيَهُودِ عَلَى رَسُولِ اللهِ ﷺ فَذَكَرَ نَحْوَهُ