The hadeeth, “There is no prayer for the one who lets his garment hang below his ankles”, and the ruling on the prayer of one who lets his garment hang below his ankles

It was reported in a hadeeth narrated
by Abu Dawood that Abu Hurayrah said: “Whilst a man was praying with
his izaar (lower garment) hanging below his ankles, the Messenger of
Allaah

(peace and blessings of Allaah be upon him) said: “Go and do wudoo’.”…
He said, “He was praying with his izaar hanging below his ankles, and
Allaah does not accept the prayer of a man who lets his izaar hang below
his ankles. (Narrated by Abu Dawood, al-Salaah, 543. This was
classed as da’eef (weak) by al-Albaani in Da’eef Sunan Abi Dawood,
no. 124). 

With regard to the validity of prayer,
Shaykh Ibn ‘Uthaymeen was asked about that and he said: If the garment
is hanging down below the ankles, then it is haraam, because the Prophet

(peace and blessings of Allaah be upon him) said, “Whatever part of
the izaar (lower garment) is hanging down below the ankles is in the
Fire.” What the Prophet

(peace and blessings of Allaah be upon him) said concerning the izaar
also applies to other types of clothing. 

Based on this, a person has to lift his
thobe (galabiyah) or other garments to be above his ankles. If he prays
in it when it is below his ankles, then there is a difference of opinion
among the scholars as to whether his prayer is valid. 

Some of them think that his prayer is
valid, because this man has done what is obligatory, i.e., covering
his ‘awrah. 

Some of them think that his prayer is not valid, because
he has covered his ‘awrah with a haraam garment. They say that one of
the conditions of covering the ‘awrah is that the garment worn should
be permissible. So a man is in danger if he prays in a garment that
comes down below his ankles; he should fear Allaah and raise his garment
so that it will be above his ankles.

Fataawa Ibn ‘Uthaymeen,
part 12, p. 306