http://revach.net/article.php?id=4314

Section: Tzedaka   Category: Lessons in Tzedoka
Tzedaka - When It's Destined To Go, There Is No Way To Hold On
Rebbi Yochanan Ben Zakkai (Bava Basra 10a) saw in a dream that his nephews were destined to lose seven hundred dinarim.  Without revealing this to them he forced them to give as much tzedaka as he could.  They gave a total of 683 dinarim.  On Erev Yom Kippur some guards came from the Emperor's palace and took 17 dinarim from them.

They were very worried that this would become a constant occurrence.  Rebbi Yochanan ben Zakkai told them not to worry.  He told them about his dream in the beginning of the year and explained to them that these 17 dinarim couple with their tzedaka of 683 dinarim totaled the 700 that they were going to lose anyway.

They then asked their uncle Rebbi Yochanan Ben Zakkai why he didn't reveal his dream to them so that they would have given away the full seven hundred to tzedaka rather than lose it to the Emperor's coffers.  He answered that he wanted them to have the mitzva of Tzedaka Lishma.

A similar story is told about a man who came drying to the great Mikubal Rav Mordechai Sharabi that he is having an operation the next day to remove a tumor.  Rav Sharabi looked at the x-rays and told him not to worry everything is fine, but he should give the cost of the operation to tzedaka.  He didd and the next day after taking another x-ray the doctors told him he was perfectly fine and the operation was canceled.

The only thing you lose by giving tzedaka is the tzorus that come with any other way the money will need to be taken from.  You can try to save a few hundred dollars here and there by not giving to tzedaka but at the end it will all be lost anyway in a more aggravating fashion, starting from a broken washing machine and busted pipe to even worse chas v'shalom.  You may as well spend it in a more productive and gratifying manner.