Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A free tileable background colored in off-white (antique white) color.
Source V. Hartikainen
This is the third pattern called Dark Denim, but hey, we all love them!
Source Brandon Jacoby
Prismatic Abstract Background Design No Black
Source GDJ
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Inspired by this, I came up with this pattern. Madness!
Source Atle Mo
Green Background Pattern
Source V. Hartikainen
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Abstract Tiled Background Extended 12
Source GDJ
A pattern formed from a squared tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
A seamless canvas texture for using as background on websites. Colored in pale tones of brown.
Source V. Hartikainen
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin