Amendment I. Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the government for a redress of grievances.
Praying is not making law, so is NO violation of A1.
Prohibiting the exercise of religion IS a violation of A1.
Amazing how so much backward thinking occurs in America nowadays.
See: Orwell, George 1984 Newspeak Dictionary