Hadith: 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

عَنْ أبي سَعيدٍ الخُدريَّ رضي الله عنه قال: قال رسولُ الله صلَّى الله عليه وسلم ِ:
«إزْرَةُ المُسْلمِ إلى نصفِ السَّاق، وَلَا حَرَجَ -أو لا جُنَاحَ- فيما بينَهُ وبينَ الكعبينِ، وما كان أسفلَ منَ الكعبين فهو في النار، مَن جرَّ إزارَهُ بطرًا لم يَنْظُرِ اللهُ إليه».
[صحيح] - [رواه أبو داود وابن ماجه وأحمد] - [سنن أبي داود: 4093]

Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) said:
"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."
[Authentic hadith] - [Narrated by Abu Daoud & Ibn Majah & Ahmad] - [Sunan Abu Daoud - 4093]

Explanation

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.