May 1st is the National Day of Prayer. 

Throughout this Nation's history, Presidents have called for a 'Day of Prayer', but it wasn't until 1952 that a joint resolution went before the United States Congress and was signed into law by President Harry S. Truman.

The National Day of Prayer is an annual observance held on the first Thursday of May, inviting people of all faiths to pray for the nation.

Fasting and prayer are religious exercises; the enjoining them an act of discipline. Every religious society has a right to determine for itself the time for these exercises, and the objects proper for them, according to their own particular tenets; and right can never be safer than in their hands, where the Constitution has deposited it. – Thomas Jefferson, 1808

The Supreme Court affirmed the right of state legislatures to open their sessions with prayer in Marsh vs. Chambers (1983).

Learn more about the National Day of Prayer.