Sheikh Sa`d al-Shuwayrikh
I am of the opinion that the woman has to cover her feet while praying.
Umm Salamah asked the Prophet (peace be upon him): “May a woman pray in a gown and a head covering without a waistcloth?”
The Prophet (peace be upon him) replied: “Yes, if the gown is long and covers her feet from the top.” [Sunan Abî Dâwûd - Abû Dâwûd comments: “Some have concluded that these words are actually the words of Umm Salamah.”]
Also, we have the hadîth related by Ibn `Umar that the Prophet (peace be upon him) said: “Allah will not look at a person who drags his waistcloth out of pride.”
Umm Salamah asked him: “What should women do about the hemlines of their long dresses?”
He said: “They may let them down by one handspan.”
She said: “Then their feet would show.”
He said: “Then they may let them down by a cubit, but no more.” [Sunan al-Tirmidhî – al-Tirmidhî classified it as a good and authentic hadîth]
And Allah knows best.
Source: Islam Today