On all bad things that happen to the public you proclaim fasts except for too much rain.

There was a story that the chachamim came to Choni Hamaagol that he should pray for rain. He told them to take in the ovens they used for the korban Pesach since they are made of clay and would be destroyed in the rain. He prayed and rain didn’t come. He then made a circle and stood there. He said ‘ Lord master of the world, your sons put their faith in me since I am a part of your household, I swear in your great name that I will not leave from here until you have mercy on your children. The rain started trickling. He said this is not what I asked for. Please send rains that fill up the pits. The rains started pouring with rage. He said this is not what I asked for. Please send rains that are a blessing. The rains started to come down nicely. It kept coming until the people left the lower part of Yerushalayim to go to the higher area in har habais.

The chachamim came back and asked him, ‘ Just like you prayed for rain to come, pray that it should stop.’ He said, ‘Go look at the rock of the strayers [where they called out lost objects] and just like that rock cannot be washed away so you cannot pray to stop the rain.’

Shimon ben Shetach sent to him, ‘If it wouldn’t be that you are Choni we would put you in cherem. However, what should we do to you who did a sin before Hashem and he listens anyway like a child does a sin to his father and still his farther does his wish.’

Taanis 3:9

If you were fasting for rain and rain came down before sunrise you don’t continue fasting. R’ Eliezer says if it rained before noon, you don’t finish fasting but after noon you finish the fast.

There was a story that they made a fast in Lod and it rained before noon and R’ Tarfon said go eat and drink today is a holiday. In the afternoon they came and said the Hallel Hagadol. [This is the hallel said by the seder on Pesach].