Reply To: Looking for a quote from Rav Volbe zt”l

I don’t know where in Alei Shur but its an open Zohar in Parshas Tazria 46b:

כמה דעונשא דהאי בר נש בגין מלה בישא, כך ענשיה בגין מלה טבא דקאתי לידיה ויכיל למללא ולא מליל

Just as one is punished for speaking negative words, he is also punished for when he has the opportunity to speak positively but did not.