All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions. 

It is permissible to drag one`s trousers on the ground provided that it isn`t done out of pride and arrogance, because Abdullah bin `Umar narrated that Allah's Messenger said, "Allah will not look on the Day of Judgment at him who drags his robe (behind him) out of pride." Abu Bakr said "One side of my robe slacks down unless I get very cautious about it." Allah's Messenger (PBUH) said, "But you do not do that with a pride."

During Jahiliyah ( The period preceding the revelation of the Qurʾān to the Prophet Muhammad), dragging garment on the ground was done out of pride and arrogance, because it was the customary practice during that period. The Illah (Legal reason) for prohibiting this practice is included in the above narration.

Based on this, Imam Al-Bukhari dedicated an entire chapter in his book "Al-Jami` Al-Sahih" entitled "Dragging Garment on the Ground without Pride and Arrogance" where he included the above Hadith narrated by Ibn Umar and the Hadith narrated by Abu Bakr. The Hadith of Abu Bakr reads as follows : The solar eclipse occurred while we were sitting with the Prophet (PBUH) He got up dragging his garment (on the ground) hurriedly till he reached the mosque The people turned (to the mosque) and he offered a two-rak`at prayer whereupon the eclipse was over and he traced us and said, "The sun and the moon are two signs among the signs of Allah, so if you see a thing like this (eclipse) then offer the prayer and invoke Allah till He remove that state." The intention of Al-Bukhari was to clarify that the Hadith of Ibn Umar is about dragging garment on the ground out of pride and arrogance.

An-Nawawi (May Allah have mercy on him) said: "The Hadith narrated by Ibn Umar is intended for the person who drags his garment on the ground out of pride and arrogance, and that Allah will not look at him on the Day of Judgment." {Shareh An-Nawawi Ala Muslim, V.2:116}.

Similarly, the Hadith in which the Prophet (PBUH) said, "What is below the ankles of a lower garment is condemned to the Fire (Hell)," is intended for the person who does so out pride and arrogance. And Allah the Almighty knows best.