Malachi 3:10 - "Bring all the tithes into the storage house, and let it be a sustenance in My Temple. Test Me, if you will, with this, says Hashem Master of Legions, [see] if I do not open up for you the windows of the heavens and pour out upon you blessing without end."
"Rabbi Yochanan met Reish Lakish's young son [and asked him]: Tell me what verse you learned today.
The boy: "You shall surely tithe..." (Deuteronomy 14:22). ["Aser t'aser" - the word aser (tithe) is repeated for emphasis] The boy: Why aser t'aser (why the repetition)?
Rabbi Yochanan: Tithe so that you become rich [A play on the word t'aser which is similar to Tit'asher = become rich.]
The boy: How do you know?
Rabbi Yochanan: Go test it.
The boy: Is it right to test the Holy One Blessed Be He? It is written "Don't test Hashem..." (Deuteronomy 6:16).
Rabbi Yochanan: This is what Rabbi Hoshiah said: "Apart from this [tithing], as it is said, (Malachi 3:10): 'Bring the whole tithe to my treasury so that there is food in my house. And please test me in this says the Lord of Hosts if I will not open the windows of Heaven and pour out a blessing on you until there is more than enough.'"-Ta'anit 9a.
So here it looks like we've got a free (actually pricey) opportunity to test God. Does anyone know any poor tithers? Are all tithers rich? Do you give ten percent, are you rich?