One source can be found in Sefer Chafetz Chayim, in the introduction, where he lists positive commandments that one may transgress when speaking Lashon Hara (Sif Zayin, pages 70-71 of Volume 1 in the link).
In a nutshell, one violates the prohibition of וּמִקְדָּשִׁי תִּירָאוּ - revere My sanctuaries (Vayikra 19:30).
I just want to clarify, this prohibition of וּמִקְדָּשִׁי תִּירָאוּ seems to be a separate prohibition in its own right (i.e. it's not an extension of Loshon Hora, but an additional prohibition that one can violate). The Chafetz Chayim included it in his Sefer to show which additional prohibitions one could violate when speaking Lashon Hora. However, one can violate the prohibition in a myriad of ways (even when the action itself might not be a prohibition on its own).