“It is Forbidden to Lie!”

The Chazon Ish, zt”l, was very careful never to promise anything to ensure that he didn’t go back on a promise if for some reason he could not fulfill it.
Even when Rav Wolbe, zt”l, asked him if he would be able to make it to the out-of-town bris of his newborn son, the Chazon Ish merely said, “I would very much like to come see the yeshiva…”
Rav Tzvi Oberlander, shlit”a, recounted how the Chazon Ish helped him in a tricky situation that seemed to require that he promise what he really could not deliver. “My elderly uncle was childless and he wanted a ben Torah to say kaddish for him. It was natural that he should try to designate me to say the kaddish. But I really did not wish to do this. As a yeshiva bochur it would be distinctly uncomfortable to be saying kaddish even for my uncle when the time came. In addition, my mother was still alive at that point and I did not know how she would feel about such an obligation. I was willing to learn mishnayos for him, however.
“I went to the Chazon Ish and explained that I wanted my cousin, who was not a ben Torah, to say the kaddish, while I would learn mishnayos for his neshamah.”
“‘So tell him you will learn mishnayos for him,’ said the Chazon Ish decisively.
“I explained that my uncle was a simple person who would not understand the importance of mishnayos. To his understanding, the main thing is kaddish. If I tell him that I will merely learn mishnayos for him, this will likely pain him…
“The Chazon Ish had been lying in bed as I asked my question, but at this he stood up and spoke in a very strong tone of voice. ‘It is forbidden to lie! It is forbidden to lie!’
“He made this statement three times and besides causing me to lose all interest in promising my uncle what I had no intention of fulfilling, this also imparted powerful yiras shamayim that lasted me for months!”