One time the Prophet (peace and prayer be upon him) said, “One Dirham [a silver coin] has outrun [in the race] 100 thousands Dirhams.”
Why? Because the one who gave one Dirham he only had two. So, he donated fifty percent of his wealth, while the donor of the 100 thousands Dirham only gave a small portion of his wealth.
So, regardless whether you are rich or poor, you can always give.
Actually, when you are poor you may potentially earn more rewards, inshaAllah.
Check out this Fifty Percent League, a group of people who believe it’s their moral obligation to give away as much of their money as they can.