Imam Ahmed Ibn Hanbal رحمه الله
said:

"Everything from a woman
is a ‘Awrah, even her fingernail,
and he said: And the fingernail
of a woman is a ‘Awrah, and
if she goes out, she cannot
show anything, not her hand
or fingernail or leather socks,
since the leather socks describe
the (shape) of the feet."

[Imam al-Khallal رحمه الله in
Ahkam al-Nisa' an
al-Imam Ahmad; 31-33)].

- أبو عبدالله الحنبلي