Ibn 'Abbas said, "Return the greeting to whomever it is, Jew,
Christian, or Magian. That is because Allah says, 'When you are greeted
with a greeting, greet with one better than it or return it.' (4:86)"
'Abdullah ibn 'Umar said that the Messenger of Allah, may Allah
bless him and grant him peace, said, "When one of the Jews greets you and
says, 'Poison be upon you (as-samu 'alaykum),' say, 'And on you.'"
Usama ibn Zayd related that one day the Prophet, may Allah bless
him and grant him peace, was riding on a donkey on a straw saddle covered
by a blanket from Fadak. Usama ibn Zayd was riding behind him. He was on
his way to visit Sa'd ibn 'Ubada. He passed by a meeting which included
'Abdullah ibn Ubayy ibn Salul - before the enemy of Allah had become
Muslim. The gathering contained a mixture of Muslims, associaters and idolaters.
He greeted them.
حَدَّثَنَا عَمْرُو بْنُ عَاصِمٍ، قَالَ: حَدَّثَنَا هَمَّامٌ، قَالَ: حَدَّثَنَا قَتَادَةُ، عَنْ أَنَسٍ قَالَ: مَرَّ يَهُودِيٌّ عَلَى النَّبِيِّ صلى الله عليه وسلم فَقَالَ: السَّامُ عَلَيْكُمْ، فَرَدَّ أَصْحَابُهُ السَّلاَمَ، فَقَالَ: قَالَ: السَّامُ عَلَيْكُمْ، فَأُخِذَ الْيَهُودِيُّ فَاعْتَرَفَ، قَالَ: رُدُّوا عَلَيْهِ مَا قَالَ.
Anas said, "A Jew passed by the Prophet, may Allah bless him and
grant him peace, saying, 'Peace be upon you.' His Companions returned the
salam.' The Prophet said, 'The Jew said, 'Poison (sam) be upon you.'
He caught hold of the Jew who admitted it.' The Prophet said, 'Answer him
with what he said.'"