Abu Dawud Book 27, Hadith Number 4075.

Chapter : Hanging down the lower garment below the ankles.

Narated By N/A : Abu Hurairah’ said: A man was praying with his lower garment hanging down. The Apostle of Allah (may peace be upon him) said to him: Go and perform ablution. He then went and performed ablution. He then came and he said: Go and perform ablution. Then a man said to him: Apostle of Allah, what is the matter with you that you commanded him to perform ablution and then you kept silence? He replied: He was praying while hanging down his lower garments, and Allah does not accept the prayer of a man who hangs down his lower garment.