The story is told about the famed Mashpia of Montreal, Reb Volf Greenglass, OB”M, who was one time standing in the hallway when the Rebbe picked up letters from the Mazkirus office to bring to his room.
As the Rebbe was walking, the Rebbe read one letter and tore it up into four pieces and put it in the garbage.
Reb Volf went right away and pulled out the letter. The letter was full of complaints as to why the Bochurim are making these props and posters for Lag Be’omer and how much Bittul Torah comes out of it.
Since then, every year, Reb Volf would help the Bochurim of the Montreal Yeshiva with preparing for the Lag B’omer parade.
In the year 5743, Lag B’omer was on a Sunday, Motzei Shabbos Bochrim were preparing for the parade, somewhere inside, but outside it was raining. Reb Volf comes inside to make his Chazoko of a plaque: שמור את השבת לקדשו.
A Bochur turns to him and says, it’s raining, what are we going to do? Instead of answering, Reb Volf says, give me the markers and placard. By the time he finished, it had stopped raining, and it didn’t rain till after the parade…