Authentic Supplication Number 229.

`Aishata said: Some Jews entered upon the Messenger of Allah  said: As-Samu alayka (may death be upon you) I thus understood it and sid: And may death, and the curse be upon you. So the Messenger of Allah  said: Gently `Aishata, Allah loves gentleness in all matters, so I said: O Messenger of Allah did you not hear what they said? The Messenger of Allah  said: I have replied with `Alaykum (upon you) (235).

(235) Replying with Wa`alaykum which means “and upon you” has been more often reported in the sunnah that `Alaykum.

`Al-`Adawee said it was sound, and that it was reported by Al-Bukhari, page 41 of volume 11 of Fath Al-Baree.