Prophet Muhammad salallahu alayhi wasalaam declared, "Every Muslm is obliged to give charity"
A man from amongst him asked, "But what if one has nothing to give?"
The Prophet responded, "Then let him work with his own hands so he benefits himself and then gives in charity"
The man inquired, "But if one is unable to do that?"
Prophet Muhammad said, "So let him call others to do good"
The man questioned further, "But if he is unable to do that?"
Prophet Muhammad replied, "So let him abstain from doing evil, for even that will be counted as his act of charity"
-Bukhari