
La Sieste probably dates from 1893. It is thought to be related to the lithograph Nude Model, Reclining c073, dating from November 1893, which was drawn in Paris. The two butterfly signatures are in slightly different form, the one at left, on the round arm of the sofa, suggesting a date of 1890/1892, while the one at right is less easy to date but may date from later.

La Sieste, Art Institute of Chicago
The drawing is catalogued in MacDonald 1995 (cat. rais.) [more] (cat. no. 1312). The entry has been revised.

La Sieste, Art Institute of Chicago

Nude Model, Reclining, lithograph, National Gallery of Art, Washington, DC
The title La Sieste, published by Drouot's auction house in 1903, means 'The nap' though obviously it could mean a siesta. The Art Institute of Chicago opted for a descriptive title, 'Reclining Draped Figure'. 1

La Sieste, Art Institute of Chicago
It is possible that the model was the first known owner, Carmen Rossi (b. ca 1878.

La Sieste, Art Institute of Chicago

Nude Model, Reclining, lithograph, National Gallery of Art, Washington, DC
The pose has been compared to Whistler's lithograph Nude Model, Reclining c073, but it is not very closely related.

La Sieste, Art Institute of Chicago
It is a drawing in lithographic crayon, with some scarping in the background and on the woman's left shoulder, and stump work that created the soft shading around the face. Numerous alterations to the outlines are apparent, and it was signed twice. It was intended for transfer to a lithographic stone but never transferred nor printed. It is on lithographic paper, papier viennoise, with a granular white-lead coating. 2
Further details are given in MacDonald 1995 (cat. rais.) [more] (cat. no. 1313).
As far as is known, it was not exhibited in Whistler's lifetime.
SALE:
1: Spink 1998 [more], vol. 1, 'Untransferred Lithographic Drawings', (cat. no. VII); Clarke, Jay A., and Sarah Kelly Oehler, eds., Whistler Paintings and Drawings at the Art Institute of Chicago, The Art Institute of Chicago, 2020, website (cat. no. 33).
2: See Spink 1998 [more], vol. 1, 'Untransferred Lithographic Drawings', (cat. no. VII); Stephanie L. Strother, 'Cat. 33 Reclining Draped Figure, 1893: Curatorial Entry,' in Clarke, Jay A., and Sarah Kelly Oehler, eds., Whistler Paintings and Drawings at the Art Institute of Chicago, The Art Institute of Chicago, 2020, website (cat. no. 33).