I heard the Messenger of Allah ﷺ say: He who lets his garment trail during prayer out of pride, Allah, the Almighty, has nothing to do with pardoning him and protecting him from Hell.  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ مَنْ أَسْبَلَ إِزَارَهُ فِي صَلاَتِهِ خُيَلاَءَ فَلَيْسَ مِنَ اللَّهِ فِي حِلٍّ وَلاَ حَرَامٍ  

while a man was praying letting his lower garment trail, the Messenger of Allah ﷺ said to him: Go and perform ablution. He, therefore, went and performed ablution and then returned. He (the prophet) again said: Go and perform ablution. He again went, performed ablution and returned. A man said to him (the prophet): Messenger of Allah, why did you order him to perform ablution? He said: he was praying with lower garment trailing, and does not accept the prayer of a man who lets his lower garment trail.  

بَيْنَمَا رَجُلٌ يُصَلِّي مُسْبِلاً إِزَارَهُ إِذْ قَالَ لَهُ رَسُولُ اللَّهِ ﷺ اذْهَبْ فَتَوَضَّأْ فَذَهَبَ فَتَوَضَّأَ ثُمَّ جَاءَ ثُمَّ قَالَ اذْهَبْ فَتَوَضَّأْ فَذَهَبَ فَتَوَضَّأَ ثُمَّ جَاءَ فَقَالَ لَهُ رَجُلٌ يَا رَسُولَ اللَّهِ مَا لَكَ أَمَرْتَهُ أَنَّ يَتَوَضَّأَ فَقَالَ إِنَّهُ كَانَ يُصَلِّي وَهُوَ مُسْبِلٌ إِزَارَهُ وَإِنَّ اللَّهَ تَعَالَى لاَ يَقْبَلُ صَلاَةَ رَجُلٍ مُسْبِلٍ إِزَارَهُ