I recently found out that four of the masekhtot in the Bavli conclude with the same drosh by R' Elazar, and that those four masekhtot are known by a special name as a result. The drosh concerns the fact that Torah scholars bring peace to the word, and hinges on the pronunciation of the word בניך. The key part of the drosh is Isaiah 54:13 - particularly the phrase, ורב שלום בניך ("great shall be the peace of your children"). The four masekhtot are Berakhot, Yevamot, Nazir and Keritot.
Although these four masekhtot are not the only masekhtot in which this drosh appears (it also appears in Tamid 32b), they are the only ones that conclude with this drosh, and were singled out by the Lubavitcher Rebbe in a hadran that was delivered in 1980 and published in Torat Menachem: Hadranim al-haRambam veShas (1992).
The Rebbe referred to them as מסכתות בני״ך (Masekhtot Banayikh), the acronym standing for "Berakhot, Nazir, Yevamot, Keritot", and alluding to the word on which the drosh itself hinges. I was impressed with this term, and don't recall ever seeing it before; it strikes me as a beautiful way to group these four masekhtot together, only I don't know where it originated!
Looking online, I have only found sources that reference the Lubavitcher Rebbe's hadran of 1980, and the hadran itself doesn't credit anybody with the abbreviation. Either that means that the Lubavitcher Rebbe invented it, or it means that it was so widely known that accreditation was unnecessary (and impossible). The Rebbe's hadran is based closely on a Maharsha on Yevamot 121b (the drosh is brought on 122b, but the Maharsha's remarks are on the previous daf), but the Maharsha himself doesn't use the expression.
So: does anybody know of a source prior to the Lubavitcher Rebbe for this beautiful expression ("Masekhtot Banayikh") - or, alternatively, is there anybody who already knew that the Lubavitcher Rebbe invented it?