The National Day of Prayer is an annual day of observance held on the first Thursday of May, designated by the United States Congress, when people
are asked "to turn to God in prayer and meditation". The president is
required by law to sign a proclamation each year, encouraging all
Americans to pray on this day.

The modern law formalizing its annual observance was enacted in 1952,
although earlier days of fasting and prayer had been established by the
Second Continental Congress from 1775 until 1783, and by President
John Adams in 1798.

John Adams (October 30, 1735 – July 4, 1826)