The Muslim's lower garment should be halfway down the leg. There is no harm - or there is no blame - between that and the ankles. However, what is below the ankles is in the Fire. Whoever trails his lower garment out of vanity, Allah will not look at him

The Prophet (may Allah's peace and blessings be upon him) clarified that a Muslim man's Izār (whatever covers the lower half of a man's body) has three states: First: The recommended state is to reach halfway down the shin. Second: The permissible state without being disliked is to extend below that, down to the ankles, which are the two prominent bones at the joint of the shin and foot. Third: The prohibited state is to extend below the ankles, and there is a fear that one may be punished by the Fire. If worn out of arrogance, gloating, and transgression, then Allah will not look at him.

1. This description and warning apply specifically to men. Women; however, are excluded from this because they are commanded to cover their entire bodies.
2. Anything that covers the lower half of a man’s body is called "Izār", such as trousers, garments, and similar clothing, and it falls under the legal rulings mentioned in this Hadīth.

سنن أبي داود (6/ 191) (4093). سنن ابن ماجه (4/ 583) (3573). مسند أحمد (17/ 52) (11010). نزهة المتقين شرح رياض الصالحين، لمجموعة من الباحثين (1/ 637). بهجة الناظرين شرح رياض الصالحين، لسليم الهلالي (2/ 95). كنوز رياض الصالحين، لمجموعة من الباحثين (10/ 582). المعجم الوسيط، (1/ 16).