Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
1- As for wiping over leather socks in wudu’, while scholars are unanimous on the permissibility of wiping on leather socks, they are divided on the permissibility of wiping on other types of socks (i.e. cotton, nylon, etc.).
2- Authentic scholars and mujtahids like Ibn Taymiyyah have affirmed the permissibility of wiping on such socks provided they are thick and not transparent.
In his response to the question in point, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
Wiping with wet hands on leather socks, instead of washing the feet, is considered not only permissible when done in conformity with the prescribed conditions but also reviving a Sunnah of the Prophet (peace and blessings be upon him).
It is making use of a rukhsah (allowance) granted to us by the Law-giver and as the Prophet (peace and blessings be upon him) said, “Allah loves people to make use of His allowances just as He loves them to comply with His commandments.” (Ahmad)
The permissibility of wiping on leather socks is agreed upon unanimously by all of the Ahl as-Sunnah wa al-Jama`ah (mainstream Muslims). That is why it has been enumerated as a matter of creed in the book called `Aqidah by Imam Abu Ja`far at-Tahawi — a work that sums up all of the creedal points unanimously accepted by the Ahl as-Sunnah wa al-Jama`ah.
However, while scholars are unanimous on the permissibility of wiping on leather socks, they are divided on the permissibility of wiping on other types of socks (i.e., cotton, nylon, etc.). Some scholars have affirmed the permissibility of wiping on such socks provided that they are thick and not transparent.
In the classical manuals of Fiqh (Islamic Jurisprudence), wiping is generally taken to be restricted to leather socks. However, there is nothing in the sources to restrict the permission to leather only.
The original intent of the permission was to bring ease and comfort; people normally wear socks, regardless of the material they are made of, in order to keep off dust and protect the feet from heat or cold.
Since it is inconvenient to take them off all the time, permission was granted by the Prophet (peace and blessings be upon him) to wipe over them for a period of one day and night for a resident and three days and nights for a traveler.
That the permission to wipe on socks or stockings is not limited to leather is the view authenticated by great scholars and mujtahids such as Ibn Taymiyyah and others; the reasoning is quite clear.
The Prophet (peace and blessings be upon him) never stated that the permission was limited to leather socks.
Therefore, the same rule can be extended to all types of socks or stockings regardless of whether they are made of leather, cotton, wool, or synthetic, so long as it is halal (permitted) material.
Coming to the specific conditions of wiping, we read in the authentic traditions: “The Prophet (peace and blessings be upon him) allowed wiping on leather socks three days (nights inclusive) for a traveler and one day (twenty four hours) for a resident.”
There are, however, certain conditions to be considered for the permissibility of wiping such as the following:
a) Socks or stockings must be thick and not transparent so that water does not seep through when wiped over.
b) They must cover both the upper and the lower parts of the feet up to the ankle bones.
c) They must be put on after making wudu’ (ablution) or ghusl (bathing), while one is still pure.
d) One must not take them off. If one does take them off, he must take the socks off and wash the feet completely the next time he makes wudu’.
e) Wiping must not exceed the period of one full day and night in the case of a resident and three days and nights for a traveler.
f) Finally, one must remove the socks if ghusl (bathing) becomes obligatory.
To conclude: It is permissible to wipe on leather and thick cotton, wool, nylon socks or stockings. In case of those who are working in offices or factories or campuses, it may even be better for them to make use of this allowance in the Shari`ah, especially where washing feet may create undue hardships or becomes a source of undue misgivings, etc. It is best for them to put on their socks after having completed ablutions in the morning; then they can continue wiping on them during the duration of their work or absence from home for a whole day or until they return home.
Almighty Allah knows best.
Excerpted, with slight modifications, from: www.islam.ca