A woman covering her feet during prayers
A Muslim woman must cover her entire body during prayers except for her face and hands. Imam abu Hanifa, al-Thawri and al-Mazsni from the Shafi school maintain that a woman's feet are not part of her 'awra [those parts of her body which not be exposed before persons to whom marriage is legal]. However, Imam Malik maintains that a woman's feet are a lesser 'awra in the sense that exposing them does not render her prayers invalid even though it is forbidden or disliked. In such a case, if the time of the prayer has not ended, she is to repeat the prayer while covering her feet though she is not to repeat them if its time has ended but she will still be blameworthy.
A scholarly contention
There is a scholarly debate on the ruling for a woman praying with her feet exposed. However the following principles of Islamic law must be kept in mind:
1- Objection is reserved for omitting what is agreed upon and not for issues where there is a legitimate difference of opinion.
2- It is recommended to remove oneself from controversial issues.
3- Whoever is afflicted with something over which there is a difference of opinion may follow the opinion of those who permit it.
Since there is a scholarly debate over the issue of a woman covering her feet, a school of jurisprudence is not to contend the position of another school in regards to the same issue. A woman must know that it is recommended that she cover her feet to remove herself from the controversy. Nevertheless, she may follow the opinion of those who permit it—she will not be blameworthy and her prayers will be valid.
This must not be a matter of dispute between Muslims because it is among speculative matters which allow for differences of opinion; and on which our pious predecessors maintained differences of opinion without it causing disunity or conflict.
Allah Almighty knows best.