The Rambam in Hilchot Melachim u'Milchamoteihem (The Laws of Kings and Their Wars), Chapter 10, Halachah 10:
"...if an idolater gives chaity, we should accept it from him and give it to the gentile poor."
Commentary: Two reasons are given as to why charity should not be accepted from gentiles:
- The merit of their generosity will prolong their rule over the Jews (Bava Batra 10b).
- The fact that Jews feel it necesary to receive charity from gentiles causes chillul HaShem, the desecration of God's name, (Rashi, Sanhedrin 26b).