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
The image is a seamless pattern of a fishnet.
Source Yamachem
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
Remixed from a PNG that was uploaded to Pixabay by gingertea
Source Firkin
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
Formed by heavily distorting part of a an image of a fish uploaded to Pixabay by GLady
Source Firkin
This is the remix of "polka dot seamless pattern".The image depicts polka dot seamless pattern.
Source Yamachem
White fabric looking texture with some nice random wave features.
Source Hendrik Lammers
This one is amazing, truly original. Go use it!
Source Viahorizon
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
You know, tiny and sharp. I’m sure you’ll find a use for it.
Source Atle Mo
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
From a drawing in 'From Snowdon to the Sea. Striking stories of North and South Wales', Marie Trevelyan, 1895.
Source Firkin
Number 1 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Here's a new gray "fabric" pattern. Use it as backgrounds for websites or for other purposes.
Source V. Hartikainen
Tweed is back in style – you heard it here first. Also, the @2X version here is great!
Source Simon Leo
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin