KNOW THAT IS not permissible to make du‘ā’ for the forgiveness of [such a person], or for anything else that is not [due] to disbelievers. But it is permissible to make du‘ā’ for his guidance, health, well-being, and so on.
We relate in the book of Ibn as-Sunnī that Anas 
said: “The Prophet 
asked for water, and a Jew gave him water to drink. So the Prophet said: ‘May Allah make you beautiful.’ He did not have a grey hair for as long as he lived.” [1].
said: “The Prophet asked for water, and a Jew gave him water to drink. So the Prophet said: ‘May Allah make you beautiful.’ He did not have a grey hair for as long as he lived.” [1].
Jammalaka-llāh.
References
[1] Ibn as-Sunnī (290).