The rate of ma’aser kesafim, giving a tenth of one’s earnings, is the average rate for a person who gives “in the middle,” i.e., who tends towards neither extreme; but a person who wishes to act generously, should separate a fifth of his possessions. This would be done in the same manner outlined above: First he separates a fifth from the principal and then he separates a fifth of any future earnings. The Sages attached this idea to the verse, Whatever You will give me, I shall repeatedly tithe [aser a’asrenu] to You (Bereishis 28:22), and from the fact that Scripture used the term “ma’aser” twice they learned that it is proper to separate ma’aser (a tenth) twice, which is a fifth.

The proper way to distribute chomesh, a fifth, is this: half of it [that is, one ma’aser] should be given to Torah scholars, and the other half [i.e., the second ma’aser] towards other mitzvah needs.