Mishkat al-Masabih #710

Abu Huraira said that while a man was praying letting his lower garment trail, God’s Messenger said to him, “Go and perform ablution.” After he had gone to perform ablution and returned a man asked God’s Messenger why he had ordered him to perform ablution, and he said “He was praying with his lower garment trailing, and God does not accept the prayer of a man who lets his lower garment trail.” Abu Dawud transmitted it.