Hadith: The Muslim's lower garment should be half way down the leg. There is no harm (if it reaches) between that and the ankles. However, what is below the ankles will be in the Fire. Whoever trails his lower garment out of vanity, Allah will not look at him

عن أبي هريرة رضي الله عنه عن النبي صلى الله عليه وسلم قال: «ما أسفل من الكعبين من الإزار ففي النار». وعن أبي سعيد الخدري رضي الله عنه قال: قال رسول الله صلى الله عليه وسلم : «إِزْرَة المسلم إلى نصف الساق، ولا حرج -أو لا جُناح- فيما بينه وبين الكعبين، فما كان أسفل من الكعبين فهو في النار، ومن جر إزاره بطَرا لم ينظر الله إليه».
[صحيحان] - [حديث أبي هريرة -رضي الله عنه-: رواه البخاري. حديث أبي سعيد -رضي الله عنه-: رواه أبو داود وابن ماجه وأحمد]

Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: ''Whatever is below the ankles of the lower garment will be in the Fire.'' Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "The Muslim's lower garment should be half way down the leg. There is no harm (if it reaches) between that and the ankles. However, what is below the ankles will be in the Fire. Whoever trails his lower garment out of vanity, Allah will not look at him.”
Sahih/Authentic with its two versions. - [Ibn Maajah]

Explanation

It is commendable for the believer to dress half way down his legs. He incurs no sin if what he wears reaches anywhere between the middle of the legs and the ankles. However, wearing something that reaches beyond the ankles subjects one to divine torment as a punishment for that. Whoever drags his garment out of vanity and arrogance, as a result of receiving Allah's successive blessings, Allah will not look at him on the Day of Judgment.