Writing at Balkinization, Jason Mazzone notes that the Westboro Baptist Church, infamous for picketing funerals for a variety of bizarre and hateful reasons, has filed an amicus brief in United States v. Windsor. That's the case in which the U.S. Supreme Court will consider whether the Defense of Marriage Act is constitutional. Normally, when briefing the issue of whether a statute violates the Constitution it is customary to refer to that Constitution, but as Mazzone points out, Westboro may now have "the surely unprecedented distinction of authoring a brief to the Supreme Court on a constitutional question that makes not a single mention of the Constitution itself."
It is probably also the first such brief to cite as authority a letter some guy in Australia wrote to the editor of the Topeka Capital-Journal, but I haven't done the research to know for sure.
To be entirely accurate, there are two references to the First Amendment in the brief, although both references appear in quotations, not the argument itself. The argument, to the extent there is one, seems to be that the Establishment Clause doesn't mean government has to be hostile to religion. That's certainly true, but that doesn't mean it has to be friendly to hostile religious people. And that's as close as the brief gets to citing the Constitution.
We do get, though, in addition to the Australian guy's letter and "Sinners in the Hands of an Angry God," citations to various books of the Bible. Most prominent, of course, is Genesis 19, in which Sodom is destroyed because, at least as Westboro interprets it, every male human being in the entire city is a gay angel-rapist, or would like to be. But Lot, being a righteous man, and—hold on. I haven't read this in a while, to be honest, and I'm just noticing this part:
6 And Lot went out at the door unto [the gang of gay angel-rapists], and shut the door after him,
7 And said, I pray you, brethren, do not so wickedly.
8 Behold now, I have two daughters which have not known man; let me, I pray you, bring them out unto you, and do ye to them as is good in your eyes: only unto these men do nothing; for therefore came they under the shadow of my roof.
(Emphasis added.) Tell you what, everybody. These guys are my guests and it would be like totes embarrassing to have you rape them, but here's an idea. I have a couple of virgin daughters to spare, so what say I'll toss them out here, you do whatever you want with them and we leave it at that? Everybody wins.
They don't give a citation for that one, but I'm sure they could come up with something.