Musar zu Dewarim 27:12

Aside from all of these parshiyoth mentioned above, which speak of the issur of lashon hara, the Holy One Blessed be He gave a special blessing to one who guards himself from this sin, and, conversely, about the man of lashon hara it is written Arur, ("Cursed"), viz. (Devarim 27:12): "These shall stand to bless the people on Mount Gerizim, etc." For all of the eleven arurim opened with Baruch ("Blessed") for one who guarded himself against it, and all of Israel answered "Amen." And then they [the Levites] said (Ibid. 24): "Cursed is he who smites his neighbor in secret," which refers to lashon hara, as we find in Sifrei; and all of Israel would answer "Amen." How much must one take care to guard himself against this sin, for which he is cursed by all of Israel. And happy is he who guards himself against this sin, for which he is blessed by all of Israel together!