Praise be to Allah.
There is nothing wrong with wearing a sock over the prosthetic leg whilst in ihram for ‘umrah or Hajj. No fidyah (penalty) is required so long as the sock is not covering any part of the body. In the case of a prosthetic foot, none of the rulings on taharah (purification) apply to it, and neither do the rulings on clothing during Hajj and ‘umrah, and so on.
If a person covers any part of his body, such as the top of the lower leg or the knee, the fidyah must be paid.
Shaykh Zakariyya al-Ansaari (may Allah have mercy on him) said in Asna al-Mataalib (1/507): If anyone wears during ihram anything that is prohibited to be worn at that time, or covers anything that is prohibited to be covered, on the basis of need because of heat, cold, medicinal treatment and the like, that is permissible, and he must pay the fidyah. End quote.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: If someone does any of the actions that are prohibited whilst in ihram, there are three scenarios:
1.. He commits that infraction with no need and no excuse. In this case he is sinning, and he must pay the fidyah for that.
2.. He does that because of a need. In that case he is not sinning, but he must pay the fidyah. Therefore if he needs to cover his head because it is too cold or too hot, and he fears harm as a result, it is permissible for him to cover it, but he must pay the fidyah.
3.. He does that and is excused because he is unaware of the ruling, or he forgot, or he was compelled to do so, or he fell asleep. In this case there is no sin on him, and he does not have to offer any fidyah." (Majmoo‘ Fataawa wa Rasaa’il al-‘Uthaymeen 24/433).
The fidyah is fasting for three days, or feeding six poor people, giving each one half a saa‘, or slaughtering a sheep. The pilgrim may choose any one of these three.
We ask Allah to make ‘umrah easy for you and to accept it from you.
For more information, please see the answer to question no. 97450 .
And Allah knows best.