We are obligated to be more scrupulous in fulfilling the commandment of tzedakah than any other positive commandment because tzedakah is the sign of the righteous person, a descendant of Abraham our father, as it is said, “For I know him, that he will command his children . . . to do tzedakah” . . . If someone is cruel and does not show mercy, there are sufficient grounds to suspect his lineage, since cruelty is found only among the other nations . . . Whoever refuses to give charity is called Belial, the same term which is applied to idol worshippers.

Maimonides, "Laws of Gifts to the Poor", 10:1-3