“You may not test Hashem your G-d, as you tested at Massah!” (Devarim 6:16)
It is a negative commandment that one should not test a prophet who us rebuking the people and teaching them the path of repentance more than necessary, once we know the truth of his prophesy, as it says “You may not test Hashem your G-d, as you tested at Massah!”. is means to say that you may not test the rewards and punishments of Hashem about which He informed you through His prophet by doubting them.
Amongst the roots of this commandment are that there is a great loss by excessively doubting the prophet, as there will always be people who are jealous of him and argue with him, and prophesy is not something constant, as sometimes he will only receive a small prophesy, and if every time we insist on him providing a true sign that he is indeed a prophet, this will cause people to rebel against him and the impact of his words will be severely reduced. We have therefore been commanded to trust him and not to doubt him too much, once we have proof that he is a good man and a faithful prophet. This actually happened with the true prophets together with the false prophets, as the false prophets contradicted the prophesies and fought with them until even sign after sign did not help.
Also included in this prohibition is that one may not test Hashem with the commandments. This means to say that one may not perform a commandment in order to see if Hashem will repay him for his righteousness, nor for his love or fear of Hashem.
Do not ask from that which Chazal said about the verse “Aser te’aser” which they explain to mean “Tithe (your money) in order to become rich, as that is an exception to all the rules, as the verse says “Bring your tithes to the storehouse and test Me please with this!”. The reason for this is that Hashem has informed us that by sustaining the servants of His house with tithes we will receive blessing in our money, and no sin will hold this back.
The reason for this prohibition is that the reward for a commandment is not given in this world, as Chazal said “Today to perform them and tomorrow (in the next world) to take the reward!”. Even though Chazal said that one who says I am giving this coin to charity so that my son will live is a completely righteous man, this is only when he decides to give the money to charity whether the child will live or not in which case he is not testing Hashem.
Amongst the laws of this commandment are that which Chazal said that the way that we can check if a prophet is a true one or not is if he predicts things which will happen twice or three times and the come about exactly as he had said. We do not need to force him to make a sign by changing the laws of nature, like Moshe, Eliyahu and Elisha. The person himself must also be an honest pious man, as it is clear the prophesy can only rest upon a man who is pious and righteous. A prophet who predicted evil to come and it did not come has not been disproven as Hashem is full of kindness and can change His mind about evil when people repent. Any prophet who predicted good and that good thing did not come about, has undermined his whole prophesy, as any good thing that Hashem predicts through His messenger, even if it is conditional, will always come about. This is from His great goodness. It therefore follows that a prophet should be tested with predictions for good.
This commandment applies to men and to women, in all places and at all times that a prophet arises for the Jews. One who tests a prophet too much has transgressed this prohibition.