"Tuesday, September 6, 1774. Resolved, That the Rev. Mr. Duché be desired to open the Congress tomorrow morning with prayers, at the Carpenter's Hall, at 9 o'clock."
Here's that prayer:
The First Prayer in Congress
O - Lord our Heavenly Father, high and mighty King of kings, and Lord of lords, who dost from thy throne behold all the dwellers on earth and reignest with power supreme and uncontolled over all the Kingdoms, Empires and Governments; look down in mercy, we beseech thee, on these our American States, who have fled to thee from the rod of the oppressor and thrown themselves on Thy gracious protection, desiring to be henceforth dependent only on Thee, to Thee have they appealed for the righteousness of their cause; to Thee do they now look up for that countenance and support, which Thou alone canst give; take them, therefore, Heavenly Father, under Thy nurturing care; give them wisdom in Council and valor in the field; defeat the malicious designs of our cruel adversaries; convince them of the unrighteousness of their Cause and if they persist in their sanguinary purposes, of own unerring justice, sounding in their hearts, constrain them to drop the weapons of war from their unnerved bands in the day of battle! Be Thou present, 0 God of wisdom, and direct the councils of this honroable assembly; enable them to settle things on the best and surest foundation. That the scene of blood may be speedily closed; that order, harmony and peace may be effectually restored, and truth and justice, religion and piety, prevail and flourish amongst The people. Preserve the health of their bodies and vigor of their minds; shower down on them and the millions they here represent, such temporal blessings as Thou seest expedient for them in this world and crown them with everlasting glory in the world to come. All this we ask In the name and through the merits of Jesus Christ, Thy Son and our Savior. Amen
The First Prayer offerred in Congress September 7, 1774 by Jacob Duché
RESOLVED, That a joint committee of both Houses be directed to wait upon the President of the United States, to request that he would recommend to the people of the United States a day of public thanksgiving and prayer, to be observed by acknowledging, with grateful hearts, that many signal favors of almighty God, especially by affording them the opportunity peaceably to establish a Constitution of government for their safety and happiness.
US Congress, 25 Sep 1789 (immediately AFTER approving the final wording of the our First Amendment)