Shaikh Ibn ul-Uthaymeen rahimahullah was asked:

Question:

What is the ruling on removing the sock or some of it to scratch some of the foot or remove something in his foot like a small rock or the likes?

Answer:

If he enters his hand under the sock, then there is no harm in that nor blame. As for removing it to see, if he removes a small portion, then it does not harm. If he removes a lot such that most of his foot is exposed, then it nullifies the wiping upon them in the future.

[Majmoo’ al-Fatawa wa Rasail (11/127)]

Translated by

Faisal Ibn Abdul Qaadir Ibn Hassan
Abu Sulaymaan