Shaykh Muḥammad ibn Ṣāliḥ al-‘Uthaymīn (رحمه الله) was asked: “Does wearing a thawb (garment) that passes the ankles nullify the ṣalāh?”
He (رحمه الله) responded:
Whoever wears a thawb that passes his ankles has committed a major sin, since the Prophet (صلى الله عليه وسلم) said: “Whatever is below the ankles is in the Fire.” (Reported by Imām Aḥmad with this wording.)
[As for the validity of the ṣalāh,] then the scholars differ over that. Some say even though the ṣalāh is valid, a man is sinful for wearing a thawb that passes his ankles. Others say his ṣalāh is invalid since he wore a thawb that is ḥarām to wear. What is correct is that even though his ṣalāh is valid, he is sinful for wearing a thawb that passes his ankles.
Source: al-Liqa’ al-Shahrī, Sitting no. 4, Question no. 15.
Translated by: Musa Shaleem Mohammed