Update, March 11, 12:30 p.m.: The rare Mary Todd Lincoln letter has been sold according to the Raab Collection.

Original post: Mary Todd Lincoln, like all mothers everywhere, had to occasionally make arrangements for a babysitter for her children. Unlike other mothers, however, she didn’t call on a neighbor but rather on Treasury Department supervisor George Harrington, who would dispatch his employee Charles Forbes.

Forbes, a Lincoln family favorite, had often been called on for child care but also would work as a messenger or body guard as needed.

An 1864 letter and the accompanying envelope in Mary Lincoln’s hand is now on the market for $15,000. It reads: “Mr. Harrington, We would like to have the services of Charles from today at 2 P.M. until tomorrow at 11 A.M.” and is signed, “Very respectfully, Mrs. Lincoln.”

The Raab Collection is selling the rare letter and envelope.

Collection Vice president Nathan Raab researched the circumstances that led Mary Washington to request a sitter for their youngest child Tad on April 18, 1864. President Lincoln was expecting to make an overnight trip to Baltimore that day to support a U.S. Sanitary Commission fair where money would be raised to help care for Union wounded. Mary was initially planning to go with him but stayed home instead, probably because the Lincolns were hosting a reception at the White House the next day and she was seeing to the final details.

Raab said the letter is rare because it was written by Mary Lincoln while she was at the White House and it is the first the company has ever carried by any president or first lady that speaks to child care arrangements.

This post has been updated.