You have no right to ask someone to commit a murder, obviously, but it's hard to say if the First Amendment protects the right to extol or encourage murder - not just murder in general but the murder of a person, or class of people, in particular. Advocacy of violence is protected speech (prohibitions on advocacy inevitably restrict unpopular political speech, as early and mid 20th century red scares demonstrated.) Conversely, neither incitement to violence nor "true threats" of violence ("where the speaker means to communicate ... intent to commit an act of unlawful violence to a particular individual or group ...") are, in theory, constitutionally protected; but, in practice, courts still struggle to define and distinguish between incitement, threats, and mere advocacy.
The state courts of Texas will get another chance in a lawsuit filed by Michael Weinstein, founder of the Military Religious Freedom Foundation (MRFF) charging that imprecatory prayers (that Weinstein's "days be few") and "virulent" anti-Semitic "rants" against him constitute "terrorist threats," proscribed by Texas law. Weinstein alleges that Elmer Ammerman, founder of the Chaplaincy of Full Gospel Churches (CFGC) and his associate, Gordon Klingenschmitt, issued an effective fatwah against him (along with Barry Lynn, executive director of Americans United for Church and State.) You can find the offending prayers, offered by Klingenschmitt, here. They include this plea:
"Let us pray. Almighty God, today we pray imprecatory prayers from Psalm 109 against the enemies of religious liberty, including Barry Lynn and Mikey Weinstein, who issued press releases this week attacking me personally. God, do not remain silent, for wicked men surround us and tell lies about us. We bless them, but they curse us. Therefore find them guilty, not me. Let their days be few, and replace them with Godly people. Plunder their fields, and seize their assets. Cut off their descendants, and remember their sins, in Jesus' name. Amen."
Weinstein plausibly claims that as a result of Ammerman's tirades and the curses rained upon him by Klingenschmidt, "threats and hate mail (against Weinstein and his family) have increased exponentially; (they) justifiably live in fear of imminent violence..."
This is not a simple case: The defendants can cite their religious freedom, as well as their free speech rights, in defense of their prayers. While they have no special religious right or license to threaten people, courts may well be less likely to find that a prayer constitutes an actual threat, which is sufficiently difficult to define anyway. People indulge in hyperbole, especially when riled. I knew someone who joked about taking a contract out on his mother-in-law. If simply uttering the words "I could kill you," were a crime, we might have to stop locking up non-violent drug offenders. This prospect of punishing people for off-hand references to murder or imaginary hit lists may seem fanciful, but in post-Columbine, zero tolerance, bullying-sensitive public schools, for example, it's not an uncommon practice. In Texas, in 2005, the Houston Press reported, a teenage girl was expelled from school for making a terrorist threat against a teacher, when she vented on an online chat room, calling the teacher "a bitch" and "a fat head" and adding "shez now the first person on my to kill list."