Tractate Taanit 9a

Rabbi Yochonon met a young son of Reish Lokeish and said to him “Read to me your verse (that you are studying)”.

“Aser t’aser – Tithe, you shall tithe (Deutoronomy 14)”

“What is the meaning of (the double terminology, it is redundant)?”

“ (Read it as follows:) ‘Aser beshvil shetisasher’ - Tithe so that you will become (ashir) rich.”

“From where do you know this?!”

“Try it out yourself and see.”

“Is it permitted to test G‑d? It is written (Deutoronomy 6) ‘Do not test G‑d’?”

“This is what Rabbi Hoshaya said, ‘(It is forbidden to test G‑d in all cases) except for this one, as it is written (Malachi 3:10) ‘Bring the whole tithe into the store-house, that there may be food in My house, and test me with this, says the LORD of hosts, if I will not open for you the windows of heaven, and pour you out a blessing, until it is beyond enough’.”

Said Rami bar Chama “What is (the meaning of) ‘beyond enough’?”

Said Rami bar Chama in the name of Rav “Until your lips are tired from saying ‘Enough…’”