Is it compulsory to wash your feet when they are clean? As In, we take ablution for Zuhr/Dhohr prayers and will be with the socks + shoes then go for 'Asr prayers making ablution but not washing the feet. Is it not permissible?
As wudu' (ablution) is a ritual washing cleanness isn't the major purpose. So once you intend to pray you need to purify yourself ritually by performing an ablution (or if necessary a full bath/ghusl or in case you are allowed or are in a valid condition by tayamum).
Note that this can be explained as a helping ritual to leave the daily life and seek refuge by Allah in the prayer so it can be considered as a tool to help us for the transfer from our dunya to our akhirah.
As the Quran quotes washing your feet (5:6) for wudu' (ablution):
O you who have believed, when you rise to [perform] prayer, wash your faces and your forearms to the elbows and wipe over your heads and wash your feet to the ankles. ...
it is an ordered (fard/farz) act!
One exception is for the case that you wear leather socks or what is called a khuf الخف (or khufayn الخفين or khufan الخفان as they are two=a pair) and have put it on after a full ablution in that case you are allowed to wipe over the khuf as long as you didn't take them off. Based on analogy (Qiyaas) some madhabs allow the same for socks (in case they are not transparent), but not over shoes as they are usually over the socks and you will take them off, as once you take off a khuf you must do ablution again.
- One can pray in shoes according some sahih narrations.
- Some madhabs consider the compulsory act to be wiping over the feet instead of washing them, because of the building of the verse.
- As long as you keep your wudu' you can pray as many prayers as you like. But performing wudu' before each prayer or after eating meat etc. is at least highly recommended.