Template:Weekday before date
Usage
{{Weekday before date|Y|M|D|W|S}} uses the optional date format string S (defaults to "F d, Y") to return the date of the first W (=Sunday, Monday, ..., Saturday) before the specified date with year Y, month M, and day of month D.
The first Sunday before September 21, 2024 is given by "{{Weekday before date|2024|September|21|Sunday}}" as "September 15, 2024".